Collapsed metatarsal arch

On my right foot, the 2nd and 3rd metatarsal heads are the lowest and I've developed quite a large callus from running.  Doesn't usually bother me when I run (except for really long runs) but does cause numbness in the ball of my foot and first 3 toes, and sometimes pain if I'm standing walking a lot, or after ~30 min of biking.  It also seems to have gotten worse over the past few months.  Also have a bunion on that foot, so not sure if there's any connection (but I'm fairly certain the numbness is not from shoes being too narrow).  Anything I can do to make it better - or at least prevent the pain/numbness?  Should I see a doc... if so, what kind?