I guess I could say I over-think a lot aswell. It traduces itself in a lack of initiative and of will to change. Generally I would say I'm lazy but I manage to find reasons for my inactivity by thinking. I have this constant inner conversation between reason and short-term pleasures where it's sometimes hard to distinguish one from the other.
When my past lack of initiative becomes very obvious, I criticise myself interiorly in the strongest ways I ever do and I feel sad for a while. The trouble is that while I'm being gloomy, introspective and harsh upon myself, I'm not being active either so in a sense I'm over-thinking aswell. It forms a vicious circle.
Fortunately this isn't always the case because I'm often busy with the duties of life (I'm thinking of school here) that force me to be productive for at least a while. Then there are punctual and rewarding moments of realisation and of awakement from the flegmatic state where I actually do things I've always wanted to do but put off for various reasons. Those moments can be the highlight of my week sometimes. Seriously, internet comments are seldom strong enough to make you act but I encourage you, if you have the same problem, to try doing all of your chores, homework and duties on a Saturday and do something you've wanted to do on Sunday. See that friend you haven't talked to for a long time, visit the library, spend the day drawing, writing, having a long honest talk with a close friends about whatever has been on your mind lately (and if you have the same problem as me, you constantly have topics to rant about in your head).
Also, to the people who seek happiness in thinking ; there is some to be had when you actually erradicate a problem just by thought, but there is more presenting your thought, sharing it and opposing it to others. You just have to find other people like you who have things to say and few people to say them to.