It sounds like you have some sort of paralysis. Work on your nerves and if you sweat bullets when you try to decide to take the trade or not, you are basically not sure about something. Go back and evaluate your strategy and have a sure entry and exit plan in place. When you trade you are often battling fear and greed, and when you are able to put those two enemies aside it will be easier to make up your mind when entering a trade.
Two approaches 1) Put on a trade on tiny size, so little that it doesn't matter at all whether you win or lose. Then slowly scale up on further trades, until eventually after a period of time you get comfortable trading full size. 3) Put on 5 times your normal size, set a stop and a profit-taking order (one cancels other), then sit on your hands until one of them is hit. After that, trading normal size will be a piece of cake.
Cutten's second method worked for me, though I didn't go FIVE times normal, just double-size. Using profit and loss targets and sitting on my hands until they're hit is the basis of all of my latest semi-automatic systems. It works wonders--I don't stress about my positions now, because I know it's all out of my hands!
pretend you already lost all money in your account, so you will be quite at ease to enter the trade since losing the second time is not so bad.