M.D.
I dont know how much formula you give him, but any amount of formula makes smelly poops. Something that you are eating, which is coming through the milk, could also be the cause of this. Or it could just be his unique digestive system.
Smelly poop is only a health concern if it is a sudden problem he did not previously have. If hes has always been like this, I would worry about his health.
Liquid poop is normal for a 2 month old. They only get solid once solid food is started, or if the baby is given only formula.