What can I do if I've received my counseling for coming off the overweight program, but still haven't been given a 4187 so I can be promoted?

TL;DR version: Hold your horses, this is VERY likely a paperwork processing issue. You will likely be promoted on 1 March, and backdated. Even then, you will not be backdated to the date you passed, but rather to 1 February - the first of the month in which you were eligible for promotion, as you were not eligible for promotion on 1 January.

Full version:
Who says you were "supposed to be promoted" in September? Contrary to popular belief, there is no such thing as "automatic" promotion. There are TIS and TIG grade requirements for promotion with waivers, and for promotion without waivers. But even without a waiver, the Commander STILL has to approve the promotion. Now... the Commander has to have a good reason NOT to approve a promotion without waivers, but it is still up to the Commander. In your case, the Commander had a good reason not to promote you - you were flagged. One you are no longer flagged, the Commander can STILL deny promotion if (s)he feels it is warranted.

You say you were counseled getting off ht/wt, but... was the flag removed? That would be the first thing I would check (or, more specifically, ask your TL to ask your PSG to check). If you are still flagged, then that needs to be removed (and yes, it CAN be backdated to the date of ht/wt pass).

I am not saying I agree, I am not saying I disagree, but... I have known many Commanders who leave the flag in place for an extra month (or even three), especially if you passed ht/wt by 0% or 1%. The reason for this is that if you come off the flag and then tape over any time within the next year, the Commander MUST initiate separation. Commanders sometimes give you an extra month to see if you can maintain, or even increase your BF loss. This is done for your benefit to prevent having to initiate a separation on you. (To be clear, this is, by the regulation, wrong. If this is the case, you CAN fight it, but think long and hard before you do. Like I said, Commanders do this to protect the Soldier, not to screw them over.)

Once the flag removal is complete, it has to be processed. This can take a few days - even longer in the times of COVID if your unit is not coming to work everyday. If the flag is not removed prior to the promotion reports being printed, it will still show you as ineligible. If you passed on the 5th and the training room was behind on their paperwork, and actually typed up the flag removal on the 8th, which then got to the Commander and signed on the 12th (long weekend), then up to S1 on the 13th, but not processed by them until the 15th, and not fully through the Army system for a few working days until the 20th (another weekend in there) ..... I am not saying this is what happened, just that it is entirely conceivable in my mind, especially if offices aren't fully operational right now (I do not know what your unit currently looks like as far as operations).

Promotion reports happen once a month. They are usually sent out around the 20th (give or take), and usually due back around the 25th (give or take). Those recommended for promotion on that report are promoted on the 1st of the following month. Unless there are VERY special circumstances, promotion orders (4187s in your case) aren't cut in the middle of the month. Sometimes they have an effective date of rank in the middle of the month (and even that is rare, anymore), but they are usually published on the 1st. If the January promotion report still listed you as ineligible (entirely possible) then you will have to wait until 1 March to be promoted. This can, again, be backdated if there was a clerical error which prevented a "proper" promotion as of 1 February.

Monthly reports are published on the 3rd of the monthly. So the reports were printed out while you were still flagged and you were marked as "not eligible for promotion." Better luck next month.

Ok, sounds like you are operating under some misconceptions. First you were under the height/weight program. Which means you were effectively flagged. Until completion of that nothing favorable could happen to you or for you, including promotions.

Promotions are not automatic. E-1 through E-4 you progress along TIG, TIS time tables and your name comes up on a list for a commander to sign off on as yes or no. Promotions are not automatic. Period. You being flagged and on a weight program effectively means you are not eligible to for promotion until the month AFTER you come off, and get the flag removed. So by your writing you got counseled to coming off the program in Jan 2021. This then has to go up the chain and be processed. It takes time. Your first official month off the program would be Feb 2021 so like SFC Casey O'Mally stated, likely March and backdated to Feb.

My guess is that your commander has been bitten a time or two and is going to wait until your next height/Weight check and see how you are doing. I have seen SM's that pass the program but backslide after the restrictions are listed.

My advice? Give it to March. Then utilize your chain of command. Platoon Sgt, then work up. In the meantime continue to lose and keep that weight off and improve as a SM and show them that you are worth keeping in and retaining. You want to be in their spotlight for all the good reasons, rather than the negative.