I am glad I came across this post, because I think I can help you out with another possibility. Look up hernias.. I found out recently that I have two small hernias in the groin area. I felt tender on one side after working out a little too hard, but otherwise, they don't hurt. I can feel them on each side, about the same size, oval shaped. They are over the pelvis bone under the skin and aren't super noticeable since they are not severe. If I lay down, they disappear (this means they are reducible).
Do yours ever seem to get smaller or disappear when laying down (don't put too much pressure on them moving them though!)? Also, try coughing and see if you notice the area slightly bulging as you cough. These are signs of hernias. When I was researching them I couldn't find ANY just like mine. Supposedly having two as a female is somewhat rare and it likely means you were born with them. I found many hernias that looked very large, and some more on the leg area, and some up higher. My doctor confirmed that they are hernias. I will be getting surgery in November to repair them. They will just be sewing up the hole in the muscle on each side and won't be using the mesh method of repair, because they are small and sometimes mesh can cause further irritation for women.
I would get it checked out as soon as you can since pain is involved. The main thing is to make sure it isn't a strangulated hernia, which means that there is tissue poking through that is trapped and squeezed. In order to save the tissue, they need to correct it very quickly. An incarcerated hernia is one where the the tissue is trapped, but not as dangerous as strangulated. Then the reducible ones are the most mild, where the hernia tissue can be gently pushed back in. Since mine was the least severe, my doctor said that not to be in a rush for surgery, but that they do recommend it when possible, and to just watch out to make sure it doesn't get worse. I also am still allowed to exercise, but no heavy lifting or strenuous abdominal exercise (I mostly just go running).
Sorry for the long post, but I wanted to share about this to give you a good idea about hernias so you will see if you think that's a possibility. It sounds very similar to what I have going on. If it isn't one, I'd suggest looking into a cyst possibility or the lymph nodes. Good luck and I hope you are able to find out soon!