I suggest that you go to see your dermatologist
or even your primary care doctor
. Things like this are hard to diagnose over the internet, but they should be able to tell right away what is going on. However, I think it is unlikely that this is something serious.
One possibility would be flat warts
, which are caused by an infection of the skin with the human papilloma virus. These are usually benign and will go away with time, but they can also be removed by your doctor.
Another possibility would be skin tags, which are small projections of skin that are caused in areas of friction, such as the side of the stomach and the armpits. They are also entirely benign, but they can be removed if they are a major cosmetic concern to you.
If the bumps you are feeling are deeper, under the skin rather than on top of it, then a possibility would be lipomas, which are small, benign fatty tumors - again, they don't need to be removed unless the become a nuisance to you.
Your doctor will be able to help you figure out which of these (or other) possible diagnoses you may have and will be able to advise you as to whether treatment is necessary.