My son just got rotatek 2 days ago. Hes been really cranky and having bad smelling poo and not eating. Is this from the vax? He also just cut 2 teeth.

Possible, but... It's possible, but studies show the rate of diarrhea after RotaTeq isn't measurably different between infants who got vaccine and "controls" who received a placebo (no vaccine). It's also possible that this is coincidental. Either way, it should improve quickly and is less likely to happen on subsequent doses. One caveat--the rare child with an abnormal immune system can have more problems with it.
Vaccine reaction. Yes RotaTeq can cause some loose stool for a couple of days, but not always . Continue to offer plenty of fluids, pedialite would be appropriate.
Unlikely / possible. The RotaTeq vaccine is given to immunize your child against the rotavirus virus which causes a watery diarrhea. It is unlikely that the vaccine would cause the diarrhea itself but there is a very small risk that it can. You should call your son's pediatrician and ask what they think. The biggest danger with diarrhea is dehydration so make sure you are giving him enough fluids.