How do you fully recover from a losing month?

I have played online poker for about 2 years and have been a decent player with .5/1 and 1/2 limit tables. Usually playing 25 hours a week and making about and average of $100 a month. However, last month just before considering moving up to 2/4, I have lost about $400. I feel that I have been playing as good as before but how do I know for sure, if I keep loosing by the end of the week after week? I have read Small Stakes Hold'em by Ed Miller, among 4 or 5 other books, and whenever I re-read it I got a little better, but I dont want to be playing with the book on my lap all the time. I know about variance and bad beats but is this normal variance? and how do you improve after bad beats? How do you keep your play strong without becoming weak-thight or loose aggresive.
Any suggestions?
PS. I know this might be better for micro-limits but I figured that the experienced ones would be already on small or higher stakes, and maybe been successful through similar bad expierences.