Can an umbilical hernia occur without a visible bulge?

I have been experiencing strange abdominal symptoms over the past few weeks. I began a cut to drop a few last pounds for the summer and almost immediately became constipated and gassy. I did not decrease my calories too much (1700 calories/day) and I’m getting plenty of fiber, fruits, and veggies; I also exercise regularly. Stool softeners didn’t work at first, but they recently kicked in and I found relief from that, but I still have strange pains and pressures that move around my abdomen and back. I’ve felt them pretty much everywhere and it doesn’t get worse after meals, but does it get better after a bowel movement.

One pain that concerns me is an on and off bellybutton pain. It’s been going on for about two weeks, so I’m not worried about appendicitis at this point, but it’s still a strange sensation. I have an appointment tomorrow with my doctor, but today I was lying flat on my back, pressed on my abdomen over my belly button, and felt a “pop” every time I did it. No pain.

I started to suspect an umbilical hernia, but the pain does not get worse when I cough, sneeze, lift heavy things, or even do ab exercises. There is also no lump or bulge visible from the outside. The pain is relatively mild and not constant.

It seems strange that I would get an umbilical hernia considering I’m not overweight, an infant, or pregnant, nor have I ever had abdominal surgery, but I know it’s still possible. Does anyone here have experience with umbilical hernias is in adults? Is there always a bulge? Could gas trapped in my abdomen cause this popping sensation?