Ive had knee pain since childhood (it would usually appear in the evening, often before changes in the weather). recently, i started feeling the same in my elbow. it seems like these pains are getting more often. what can it be?

Joint pains that are worse in the evening are usually related to mechanical issues; that is, rest and then proper posture/position, muscle strengthening can help. You will need to see a doctor to examine you when symptomatic to have a better idea.

Certainly it makes sense to have a full evaluation by your doctor. That would involve a physical exam & possibly lab work maybe X-rays. Although this may be overuse, different types of arthritis should also be investigated.