Seems to me as if you're just losing frequently, make it to the point where you're playing with small lot sizes and winning on a frequent basis then move up...Try to average 7/10 trades and keep it consistent everyday ...take nothing but high probability trades in your demo until you reach a point of 7/10 wins and 8-9/10 wins then your lot size shouldn't matter from there.
Manage money in forex need plan trading, which as trader also will calculated about risk management in every single plan, and trade with proper money managemengt, trade with high risk taker might will obtained huge profit but also will harmful account shortly