Is the Good conduct service medal automatic? I'm at 37 months yet I still don't see it on my ERB. How do I get S1 to award it?

It is automatic but not automatic. For example, you could be at 35 months TIS, nothing bad until one day you get an Article 15. Boom. Clock restart. As long as you stay out of trouble, you'll get it, just as soon as the Commander signs the paperwork. Get with your NCOs to shoot this RFI up the Chain.

Every month the commander receives a report (AAA-199) of personnel in the unit that are eligible to receive the AGCM. They circle Yes/No and sign the report then return it to the S-1. After that the S-1 or MPD will produce award orders and a certificate and return it to the unit. Give it about 2-3 months to be processed. If you still don't receive anything, then bring it up.

AR 600-8-22, Military Awards, Chapter 4.

"The Army Good Conduct Medal (AGCM) was established by Executive Order 8809, 28 June 1941 and was amended by Executive Order 9323, 1943 and by Executive Order 10444, 10 April 1953. It is awarded for exemplary behavior, efficiency, and fidelity in active Federal military service. It is awarded on a selective basis to each Soldier who distinguishes himself or herself from among his or her fellow Soldiers by their exemplary conduct, efficiency, and fidelity throughout a specified period of continuous enlisted active Federal military service, as outlined in chapter 4, AR 600-8-22. There is no right or entitlement to the medal until the immediate commander has approved the award and the award has been announced in permanent orders."

https://www.hrc.army.mil/content/Army%20Good%20Conduct%20Medal%20AGCM