I fractured my 2nd metartarsal in my right foot 5 weeks ago whilst running. It is a complete mystery as to why and how it happened. As I started the run I had a dull ache at the top of my foot which I ignored and carried on running. By mile 5 the pain was so severe I had to stop.
My advice is that even if you have a very small pain in your foot stop immediately as you can worsen the break.
I still use crutches 5 weeks on but have been told I can introduce gradual weight bearing. The pain does not seem as bad.
I really sympathise with anyone who has this. It has driven me mad and still is and is the most frustrating thing to go from exerciing reguarly to doing nothing at all.
I also advise that you rest your foot as much as possible until you go back for an x-ray after 5 weeks.
I'm going to start cycling and swimming which are supposed to be very good to maintain fitness. I would also recommend going for walks on your crutches in the first 5 weeks with keeping your injured foot completely off the ground. When you get used to this introduce a hill. This is certainly a workout in itself and is better than no exercise at all. Getting the blood flowing is supposed to aid the healing of bone.