There are several reasons why this might happen. You might be developing a cold, there might be debris on the lens, or even a nick in one of the edges.

If you haven't cleaned your lenses properly, there might be some deposits left behind, so be sure to clean them again.

If your lenses have been cleaned, start by rinsing them thoroughly with saline or an all-in-one cleaning solution to remove debris (never use water or solutions that are not designed for rinsing).

Examine the lens carefully for nicks and tears and if it's damaged, throw it away.

Never continue to wear a lens that is uncomfortable or irritates your eye.