What Could Be Causing Pain, Swelling, And Altered Sensation In The Back Of My Hand And Forearm?

Hi, please help me. I have been feeling a little pain on the back of it (not the palm side), pain then escalated to swollen blood vessels while radiating to the wrist and forearm. Compared to my other hand, sensation is also debilitating, if I touch my fingers I fell like a very small insect is sitting on them whereas on the other hand everything is perfectly normal. The hand is still fully functional, no other symptoms, no underlying disease, no family history of anything like this What could be causing this? Could I lose all sensation in the fingers? How can I stop thing from progressing any further?