I burn very easily in the sun and sometimes i get bumps that look like poison ivy on my arms?

this hasn't happened in a few years but i was in the sun yesterday and they're back. i put sunscreen on repeatedly and i still have them. most of them are just small red bumps, but there are 2 on my hand that are white bumps. they used to go away by the fall. i only get them in the summer. anyone know what this could be?