OCD does come and go in waves. factors are lack of sleep (fatigue), hunger, stress, mood, hormones, etc. those things usually cause OCD to rear its ugly head. when you are most vulnerable is when it attacks.

and you will get stronger. the more you resist, the stronger you will be because you will have shown OCD that it does not rule you. i know its hard. but it does get easier, i promise. what you are doing when you resist is laying new pathways in your brain. so that next time OCD tries to grab you, you will have a new path instead of the path that causes you to compulse. I dont know if I made any sense right there lol, but the bottom line is that OCD is a neurological disorder, a brain fart if you will... but by resisting, you can change the way that the brain is wired and redirect those thoughts. Like anything, it comes with practice...