Dwarf gourami sitting at top of tank?

I have had him for a few weeks now. He used to swim all over in the front of the tank. A few days ago he started sitting at the top in the back corner where the filter is. He swims around at feeding time but goes back to that spot. I don't know if he is hiding or sick? He just doesn't seem to be his happy slef. He was eating betta pellets and blood worms and I just got some tropical fish flake food. Was I feeding him the wrong thing and it making him sick? He has lots of places to swim and hide because my tank has a huge fake tree trunk and plants. It is 16 gallons and he shares it with a platy. I don't think the platy could be bothering him but who knows, the tank has been running for two months and I do weekly water changes also.