OP: Fortunately, I never got to the tubes-bursting stage, but I had low (but doubling) betas, no sac visible in the uterus though I had 3 ultrasounds during week 7, and extra fluid in the cul-de-sac (the space between the 2 fallopian tubes). I also had near-nonstop spotting from week 5 to 7. We treated with methotrexate at week 8.
Cramps could be just about anything, so I wouldn't read too much into them. You're being regularly monitored, so if it is something unfortunate, like a suspected ectopic, they should be able to catch it right away.