first off put a call into your doc...the pain could be a cyst (no big deal) or another problem...i think if it was ectopic the pain would worsen but i cant really say for sure.
there is a board on her for ladies using injectables have you fentured there? they can help you more there on that topic.
by this point they should be able to see the sac. i had my first u/s aound 7 weeks and my lil bean was there as clear as day
if the pregnancy is in your uterus and is visible i think i would wait it out...being closely watched of course.
have you asked for an u/s yet? let me know if you call your doc and what they have to say
be persistant this is your body and your lil bean