My right middle finger suddenly gets stiff and it begins to swell in the center, so. after a few. minutes it starts to go down and it looks blue?

Achenbach's Syndrome: Hard to say for sure without exam but it sounds like something called achenbach's syndrome. Usually caused by leakage of blood from bursted vessel, resulting in a bruise. Sometimes a minor pressure from activity such as griping may bring it on. No definite treatment but ice pack applied at onset will help. See your doctor for further eval and reasurance.

?Raynaud's?: This sounds like raynaud's phenomenon or some other vascular condition. I would discuss with your physician because it should be evaluated.