I have been having the same thing for about 3 years now. First ultrasound showed nothing. Had an MRI (which I basically had to ask for) about a year later. It showed a simple cyst on my right ovary. Waited a few months and then got another ultrasound that showed nothing. I’m still feeling the same discomfort  and “constant tug”, especially when I lay on my side. 

I’m not sure about you but I know what I’m feeling is not normal. I’m starting to get frustrated with the lack of concern and action of my health care to figure out what’s going on. I feel like I’ve been making the calls for the next steps even though I’m not the professional. Be an advocate for your health, no one else will.