How to fix a messed up LG Optimus?

I have an LG Optimus by Tmobile. Lately I had been getting some notifications saying that I was low on space,(which is strange because I have not downloaded a single app and only use facebook) so I cleared the data from some apps that I didn't use and it seemed to do the trick. However, I got the notification again today and cleared off some more, accidentally clearing the email app. And then my phone just freaked out. I keep getting these little popups that say "Android phone not working" and "android messaging not working". I can't use anything on the phone, and the popups themselves are so frequent that I couldn't get to anything even if I tried. I'm desperate. How can i fix this or reset anything? Any advice welcome!!