ectopic pregnancy?

I had a pelvic MRI done to look for the cause of my pelvic pain. I'm so worried that I'm pregnant.. I would have had the MRI done at 14 weeks. If I had an ectopic pregnancy would it have showed on the MRI? 
I can feel a lump on my left hand side of my abdomen in between my hip and belly button. I would now be 18 weeks. I'm really scared. 
I have taken 12 pregnancy tests and they have all been negative... If I had an ectopic pregnancy would I still get a positive test? my doctors haven't ordered any blood work to check for pregnancy because I have had negative tests. 
PLEASE HELP IM VERY WORRIED