The best source of forex earning is patience and knowledge, this market is highly volatile, if you don't understand the risks, you will lose your funds quickly.
You should trade with in demo with the trade size that you would actually prefer in the live trading. If you are making loss that is not just dependent on the lot size, your trading strategy and skills matter.
Demo accounts are really great for learning and experience, but what you feel while trading in a live account is not what you feel in a demo, as no real funds are involved in demo