Hi N. - isn't it frustrating?? I've been dealing with FUN fertility problems for #2 as well....I feel your pain!
I've taken Prometrium, but not to induce a period. My doc describes Prometrium as the "voodoo drug" - meaning yeah, it may work, or it may not, but if it makes you feel better to take...I've had trouble keeping pregnancies, so Prometrium is supposed to help in those very early days of pregnancy. She has me take it right after I ovulate. She put me on Clomid to force ovulation, though. She had never mentioned Prometrium, though I do know some docs prescribe it. Are you testing for ovulation? That may really help.
Because of your age, if you're not pregnant in the next 3 months, you should seek the help of an infertility specialist. I'm 34, and actually have been trying for a very long time (after a wam bam quick conception with my first baby, too), but my doc and I just now made the decision to get me over to a specialist.
If you decide to go that route, so far I really like my specialist - Dr. Barnett in Plano - one of the top 10 infertility clinics in the US. It took me 2 months to get an appointment, but it was worth it.
Good luck! And hey - at least it's fun trying, right??
S.