I have had the same problems as you describe when I play NL. I'll play well until I have the 2nd best hand and then lose my buyin. My suggestion is get your feet wet playing Sit-n-Gos and other tourneys. This limits your risk, gets you the experience and you can build a BR with it. If you play in a $2 MTT for 3 hours and don't get in the money you still got to see a couple hundred hands/scenarios for $2.