If it is PF, you can buy arch supports in Boots for about £25 - by Orthoheel (?) I think. Bought some last year, wore them in all my shoes for about 6 months, now OK. Just have to wear the sport ones in my running shoes because otherwise I get pains in my heels.
Good luck, but whatever it is I wouldn't leave it unchecked. GP's have a fairly brutal test for PF, but it does leave you in no doubt!!:o