After I branch infantry, will I have to earn my blue cord again during IBOLC or will I be able to wear it since I was 11B enlisted?

The blue cord is an MOS/AOC and duty position dependent award.
You were authorized to wear it as an 11B in an 11B duty position.
Once you started OCS, you became 09S, and upon completion of OCS, 00D.
You will not be 11A until graduation day of IBOLC, upon which, assuming your duty position back home is 11A, that will be the first day you are authorized to wear the blue cord (again).
In reality, you won't be branched 11A until your G1 OPM gets a copy of your 1059 and codes you 11A a few weeks or months down the road after graduation.

I was 11B enlisted, as we several of my class, and they wouldn't allow us to wear it back when I went through IOBC. I was pissed about it.

Infantry Basic Officer Leadership Course has a "Cording" Ceremony and Graduation Ceremony. This video covers the cording which takes place a day before graduation. This is a bit dated 2011 however.

https://www.youtube.com/watch?v=_TkJ6EiisPM