Over the last couple months, my skin itches and when scratched it swells and leaves bumps, almost like an allergic reaction what can be causing this?

Lots of things. There are a number of possible causes of itching;it's a good idea to see your doctor to determine the specific cause and any treatment needed.
Dermatographism. Your description is consistent with dermatogrpahism (literally, writing on the skin). The pressure of scratching triggers release of histamine. This is the chemical responsible for hives and a number of allergy symptoms. Usually, there is no external cause but an investigation with your doctor is worthwhile.