My baby lost some weight!

We recently adopted a little kitty boy from one of our area rescues (born 9/25). The foster mom said she was confident he was ready to come to a home, but now I am seriously doubting her. He came to us with a cold about 11 days ago. She said once he settled in, it would go away. Took him to the vet on day 2, vet said he had an ear infection and something going on with stinky poo. He dewormed him again, gave us ear drops, and probiotics. I took him back today and he has gone from 3.03 lbs, to 2.7. We have no idea why! He is eating Blue kitten food (wet and dry). Doc sent us home today with antibiotics for the cold, some for possible parasites, more ear drops, vitamins, more dewormer, and more probiotics. Anyway, he wants to do blood work too, but we were after hours already so are waiting for another day.

Any tips for getting him to gain some? Some of the possibilities the vet went over sounded scary - I'm really hoping he just needs some drugs and tlc!!!

Both parasites and an URI can cause weight loss.  Once the parasites get taken care of, that will help.  Kitties won't eat or will eat less if they can't smell, so if he's congested, he won't eat as much because his food doesn't smell.  You can warm up his wet food with a little bit of warm water added to it or warm it in a water bath or for just a few seconds in the microwave.  If possible, you could try offering him wet food throughout the day.  When my cat was a kitten, we fed him about 6 small wet food servings a day and supplemented with dry.  If you're really concerned, call the vet and ask for Science Diet a/D.  It's got tons of good nutrients in it and can be slightly addictive.