"New hearing aids"

I had new instruments about a month ago. At first I thought there was quite an improvement but I noticed that the ear pieces were bigger than the previous ones and they were a bit uncomfortable to wear. After about a week  I swapped the pieces over to the older smaller ones which are more comfortable but don't seem to work as well. I don't know if the new instruments (oticon) are self adjusting as far as volume goes because I also seem to have quite a bit of feedback in the right ear.