What would happen to my eyes if I force them and cause eye strains regularly?

I'm nearsighted and I have a pair of gles. I'm tired of them but can't get contacts (my eyes become red and dry and I'm also extremely afraid of putting them in). Now for a few days, I've been squinting to see the board, refusing the aid of gles and they have caused headaches. Am I doing something dangerous to my eyes? What could happen to it?