I got level two frostbite on both of my hands and they constantly swell up. Whats the reason for this?

Lymphedema. You may have had sufficient injury to the lymphatics that they are not functioning well. You probably would benefit from compression therapy and then compression garments to control the swelling.
Lymphatics. Your lymphatic vessels have likely been traumatized. I would recommend a compression garment for your hand and arm. Prior to that you should seek the opinion of a vascular specialist about lymphedema treatment.
Vessel overactivity. Frostbite alters response of the small arteries to cold: they tend to become hyper-reactive and constrict with repeat exposure to cold. This gets better overtime, but very slowly. Best strategy - avoid exposure to cold - use warm gloves or mittens.