Why do I keeping getting painful bumps when I sit in the sun?

Sensivity. U might be sensitive to sunuse sunscreens.
It depends. Many medications (both oral and topical) can cause a photosensitive dermatitis (rash due to sun exposure). Topical sunscreens can also cause this problem. In addition, photosensitivity can be seen with certain genetic conditions (such as porphyria) and autoimmune conditions (such as lupus). Rarely, individuals can develop hives with sun exposure. Discuss with your healthcare provider.