A red bump that comes and goes is often times a small cyst or pimple. We can get these anywhere on our body including the genitals.
Some glands can get clogged and infected causing a pimple to appear. These often clear up on their own once the body eliminates the infection. You can help speed up this process by applying a warm washcloth to the area or bump. It may also help to take warm baths. This improves blood flow to the area, which speeds healing. Occasionally the body doesn't fight the infection well on its own and needs some help from antibiotics.
Cysts have tough walls and may need a doctors help to get rid of them. They can simply swell without pain, or become infected like a pimple. Warm compresses may or may not help.
In either case, if you have a bump that is getting larger and redder, it is likely infected and you should see your doctor to see if it needs to be drained or treated with antibiotics.
Read Bumps and Lumps: When Do They Require Medical Attention