Most Helpful Guy
It's an anxiety problem. Get counseling
Most Helpful Girl
Oh, this sounds exhausting! I know how it's like to do things obsessively :D
My advice would be to find a way to remind you that you don't want to do it. For me, it has helped to lock the apps I wanted to use so that I have to actively unlock the app (I had problems with Internet addiction...)
This helped me a lot because then I had to wait for a second and think "hold on. I locked this for a reason. Stop. Close the app. Do something different"
Maybe you could try something like that, too? Maybe put little slips of paper in your purse or another spot where it's visible to you as soon as you want to shop something, so that you are reminded to not do it.
For the online shopping, you could try to lock or disable those websites if you want to stop shopping very badly. Try to reduce the possibilities for you to spend money on cloths etc :)