Lower abdomen growth

Hi everyone. I am a 30 year old male. I really have no major diagnosed medical problems. Here is my issue : I have always been extremely thin. It runs in my family, so it is normal. About 2.5 years ago, I started to notice that for no apparent reason, the lower right part of my abdomen seemed to be enlarged. No pain, no redness, and really no discomfort; barely even a "mass".....just larger than it was before and larger than the left definitely. I had gone to the doctor, had an ultrasound done of the stomach down to the abdomen, and nothing was found. Blood tests were pretty normal. Now after 2.5 years, the right side has gotten even larger (though not huge and not noticeable from a distance, but definitely noticeable up close), one with some discomfort (still no pain), and slight tenderness if pressed on. I can feel slight pressure in that area and it just feels like something is there almost like if someone taped a little marble to my skin. What it also feels like now; is as if there is a slight fluttering movement somewhere between my inner upper thigh, into the groin area and into that enlarged area in the lower right abdomen. It could even be pressure near or under the testicles. It is really tough to pinpoint where exactly this pressure and discomfort is coming from! Still nothing painful, but just a weird feeling like a pulsing vibration every so often. Also worth noting is that on the right side, when I tap on it, it sounds hollow and like a bongo, while the left normal side just feels like any other area of the body when tapper on. One more thing is that while this has occurred, I have grown a belly which feels somewhat hard (this is strange because I have never ever had a belly in my life and being so skinny, it sometimes was as if my belly was caving in even!)

Any ideas ?????

Have you been to the doctors since the swelling increased further? I'm no expert and have no idea what to tell you but if you haven't gone back to the doctors since the increase in size I'd say go again... If it doesn't show up on the ultra sound then it can't be something solid which might mean it has something to do with fluid but like I said I'm no expert. Hope this helps.

How are  your bowel, do you poo regularly? 

Yes, normal bowel movements and no stomach issues or stomach pains

I would tell dont worry but obviously you are so do so get a second opinion.Dont ket it get to a point of pain.

Did you ever find out what this was!? I have the exact same and am so scared!!