Can surgical screws come loose? I have a screw in my big toe from a surgery to fix my dislocated big toe and bunion. I feel pain and grating lately.

YES. THEY COULD BECOME LOOSE. IF YOU FEEL PAIN YOU SHOULD SEE YOUR SURGEON ASAP. GET IT REMOVED OR REPLACED IF NEEDED.
YES. Yes, fixation can loosen. Get an xray from your surgeon.