Keep getting pain in my lower left calf, shooting/throbbing. veins look thick in lower legs. foot swells. what to do. what can it be.

Possible clot: Not a diagnosis i like to make without an exam. However, these symptoms can be associated with deep vein thrombosis (dvt). It would be unusual unless you are taking bc pills or your are pregnant. This condition is associated with migration of clots to the lungs. So, i recommend you see a doctor or go to the emergency room.

Leg swelling: If you are having sudden leg swelling, able to palpate a cord like area on your calf, and pain you need immediate evaluation to make sure you don't have a blood clot. This is not very common at your age but it can happen nonetheless. Anyway, I am lacking a lot of information on what happened prior to the onset of your symptoms. Try to get to the nearest ed or urgent care center asap.