I think that you should schedule an appointment with a gynecologist. If you think there is a possibility that it is an etopic pregnancy, then you need to go to the ER ASAP. If it is an ectopic pregnancy, it could be a life or death situation. They would do a transvaginal ultrasound to see if that is what it is and they would be able to see if it is a cyst at the same time. I think that would be your best bet, as an ectopic pregnancy is nothing to play around with. Please let us know how you are doing and what you find out.
could it be ectopic even if the pregancy tests come back negative
Yes. Sometimes the test is negative and there is still an ectopic pregnancy. Here is a website i found that may be helpful to you.
http://www.webmd.com/baby/tc/ectopic-pregnancy-symptoms
hope this helps!