dd is 8 months next week and is just under 16 lbs. I always here "oh, my she is almost 8 months, what a small baby!". It used to irritate me and still does sometimes, but if she was 8 months and on the chubby side, then people would comment about that as well. As long as ped is ok then I wouldn't worry about it.
dd has always been a small eater, with her formula and with her solids. I used to get really worried when I would look at all the feeding schedules on this site for other lo's her age and see how much they were eating!!! But, she is gaining weight and I can't force feed her so all is well.
Just wanted you to know you are not alone.