Pain from not wearing retainer?

I haven't been wearing my retainer properly (just at night) for the last 3 months. A few weeks ago, I decided to put it back in because I noticed a small gap forming between my front teeth. I did some research and it said that if it still fits I should start wearing it again. It's not that my retainer hurts I'm just having trouble getting used to it again so I've only wore it for about 2 hours every night starting about a week ago. Today around 5:30 I noticed that my mouth started to hurt even though I'm not even wearing my retainer. What is this? And will wearing my retainer all night tonight make it worse?