I had that happen at 9 weeks. everything turned out to be fine, but my doctor did send me for an ultrasound because he was afraid it may be placenta previa. It wasn't, but if it was there are some precautions to take. Have you talked to your doc/midwife about it? I would give a call; its better to be sure.
I had this at about 14 weeks, and then had a regular pregnancy and gave birth to a 9-pounder who will turn 2.5 years old this weekend!! However, my dr. took me off all exercise for a few weeks because of it. I don't think it really makes a difference.