I've had some arch pain the past few runs, just in my left arch. From what I can find, this appears to be a fairly common issue, and I suspect it could possibly have to do with changing shoes. Though that is not the only possible cause, it seems quite likely. My new shoes have less arch support than my old ones.
I did try going back to my old shoes, but the pain still manifested. It happens after I complete a run and then sticks around after, gradually getting better.
This pain has gone beyond "niggle", so I'm trying to be very careful with it because I really don't want to end up with a serious injury. These are the helpful bits of advice I'm following:
1. Ice it after each run, about 20 minutes.
2. Roll a ball under the arch. (They say tennis ball, but I took the ball out of my cat's ball-track toy since it's close in size and I didn't have a tennis ball on hand.)
3. Lay off the speed work. (Argh, I hate this one! Speed work sucks, but it reallyyy helps my times.)
4. Go easy on the pace and distance. (Careful with the "comfortably hard", sticking more on the side of just "comfortable".)
5. Take a day off if the pain is worse than normal and your body is telling you not to run.