It could be something as simple as gas moving through your intestines, or something more serious.
Do you have any pain when you feel these movements? If not, I would think it's probably gas, and not worry about it.
If you are having pain, or, if your stomach starts getting larger and feels somewhat hard when you push on it in certain places, it could be a tumor. When you stand up from a seated position, does it feel like something heavy inside 'drops' in your abdomen? Do you ever feel a severe pain, or feel like you can't walk without help?
I ask those questions because, after my last c-section, within a few months of the surgery, I started having pain in my abdomen, and when I would stand up, it felt like a bowling ball would drop in my stomach. I often was in severe pain, and sometimes I couldn't walk without help.
I went to my ob/gyn over and over and he kept telling me it was a pelvic infection. I insisted it wasn't, but took the pills (over 60 antibiotics in total while seeing this idiot), and finally I got a second opinion, this time from a gastrointerologist.
As soon as I laid down on the table in the gastrointerologists office, he said he knew something was wrong, and immediately ordered a cat scan. I am overweight, myself, so my stomach should have 'spread' out a little flat when lying on my back. It did't - it stood straight up.
Well, turns out I had a very large and very fast-growing dermoid tumor or cyst as some call it. The pain I was feeling was something called 'torsion' where the tumor was being twisted around inside of me by the things attaching it to my ovary. The 'drop' feeling I was having when I stood up really was the tumor dropping inside my body, and the difficult walking was from the pressure of the tumor on my pelvis.
The tumor ended up being about 12 pounds. My last baby was 9 pounds...they had to cut my c-section scar larger than for my baby, just to get this thing out. They also had to remove my left ovary. If I had not sought a second opinion, it would have kept growing and could have burst at some point.
The point is, if you feel something is wrong, don't take just one doctor's opinion. Go to as many doctors as you need to. If you haven't already seen one, make an appointment right away.
Could very well be just gas if you have been eating a lot of high-fiber foods lately, but it could be something like an ectopic pregnancy or whatever. With my tumor, it was made up of hair, teeth and skin tissue among other things. It felt like a baby moving inside me. Very weird and freaky when I knew I couldn't be pregnant...