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.