how to get bitcoin again if it's gone and it's gone because of scammers
That's really a one way process and you can not get the bitcoin once you send it from your account to the other. The peer to peer system is made like hat way. You can get it back if they think of reverting it to you.!
I used to invest in sites I know I can earn too much
When there comes too much earning, or the sites claiming that they will make you rich with small investment then they are most probably scam and you are not going to get the money.
but I do not know most of those scammers,
That's the first thing, you should know where are you investing and what are the option if you get scammed.
I earn here without very little money
Little money is always good as long as it is legit one.