I think I've cracked my fiiling, what do I do next?

I had my lower 6 and 7 filled with composite resin two weeks ago. Yesterday while chewing I felt discomfort/slight pain in that area and still do, like something is stuck between my teeth. I think that filling on 7 cracked but I'm not really sure - I don't see anything suspicious in the mirror. I went abroad few days ago so I can't meet the dentist who did the job for emergency visit and I will have to wait at least a month before visiting the local one. Those are pretty big fillings so I'm afraid that tooth pulp might be in risk of rot and infection.

I have a few questions:

1. What signs should I watch out for to know if my filling is truly cracked?
2. How long can I safely go without getting it fixed?
3. How do I protect tooth with failed filling? What should I avoid? How treat the tooth?
4. How will dentist know if my tooth is truly cracked (jaw X-ray or some other method)?