Ok firstly 5.5 inch girth is nothing to sniff at. Just go look at official condom size stats and you will feel much better. I think the average length is a bit less than 6 inches and the average girth is also under 5.
Anyway the sense of inadequacy you have now, may not even go away with a bit more size so try to nip that in the bud. Be happy with your level and the fact that you WILL get bigger if you go slowly and surely. A desperate need for a quick fix is a recipe for frustration, low self confidence and injuries. The trick for me is to be happy with it and still want to be bigger. You will see that some guys are really big and yet they are still here improving themselves. Slow and steady wins the race.