I know exactly how you feel!!! I hate it. :[ When I was going through a break-up and having a rough time, I didn't want anything to do with people. Then one of my friends said that I should go to the school dance. I agreed and had such an amazing time! I was so glad that I went. I was sooooo happy!!! ^_^ Well....for a while at least. All the bad memories started to come back again and I was sad...again :[ It's very frustrating for me. I tried getting the good memories to came back and think about happier times. It never worked. It took a while but I was able to stop thinking of my past relationship.
I'm also ALWAYS anxious and thinking about something constantly. Which make the bad memories worse. I hope you get through this better than what I did. <3 You'll be in my thoughts :]