Hi K.~
I had the same problem--my almost 3 year old went in the potty a couple of times, then it was always "soon mommy, soon". You didn't mention what he is wearing during the day--is he still in diapers, pull-ups or training underwear?
Once I switched my son to the training underwear, made of cotton, but thick to absorb pee with accidents, he began using the potty soon after. Most kids don't like being wet, yet this avoids big puddles on your floor.
I too tried using a sticker chart, but realized the goal was to abstract. I then made 10 circles on the chart, and drew a picture of him on the potty at the top, and a picture of McDonalds Playland (his reward) at the bottom. Whenever he used the potty, we would put a sticker in one of the circles. Being able to see how many circles were still needed to get McDonalds seemed to work very well for my son. Once he got a playland trip, I then just began giving him a couple chocolate chips whenever he'd use the potty, and after a couple of weeks, phased them out too.
As for pooping--for a while he would not use the potty, even though he was peeing in it. Finally, I just left him in only a shirt, and told him "don't poop on my floor" and the first time, he pulled a diaper out of the drawer, opened it up, and then pooped on it! and said "I didn't poop on your floor mommy" (sigh) After I made a big deal about how gross and stinky that was, and showed him how I flushed it anyways, the next day when I left him naked, he used the potty, and has been ever since.
Good luck, hang in there and it will happen. The new baby has got to factor into it, so maybe pointing out all the big boy stuff he does that the baby can't do will help get his mind thinking that he can do it.