Hello guys

i have had this guy for like a couple of months now.. He s 4 months old and was fine until 3 weeks ago when he started to swim lopsided and gradually started to sneeze , gape and yawn a lot expectorating white mucous. Needless to say it was a full blown RI . I live in India and there arent a lot of vets around let alone reptile vets.. I managed to show him to one of em but he couldnt help me. i have this lil guy in a 50 gallon tank at the moment with a water heater and basking light. I cant get a uvb lamp here so i let him swim around in the sun in a tub as often as possible. Water temp at the moment is 75 F and basking temp around 90F. I called up a vet who knew bout turtles in another city and he asked me to put him on a course of ceftazidime. I calculated the dosage based on his weight and injected him day before on his left front leg IM. I am a medical student for the record so giving shots arent as difficult. Its been 2 days now.. His symptoms have lessened.. Doesnt sneeze as much nor does he yawn or gape either.. But the prob now is he just wont sink now and just floats around like a bob.. This happened after injected the day before.. Is it a mere coincidence or something i did? Am worried

he seems lethargic , basks and sleeps a lot.. His appetite has diminished but still eats. Help!