Then it is much better for me to save my bitcoin for now and wait after the halving? Is it still advisable to invest on the mining sites after the halving?
If you haven't gotten the point yet, here it is: don't invest in mining sites.
They are ponzi sites that will eventually collapse and run with your money; if the cloud mining sites are legit, then there is practically no way that they're profitable. Just steer away.
If not, how can I earn more Bitcoin after the halving if most of the mining sites will stop operating?
You mentioned one way up at the very top; start trading bitcoin. It can be a risky business (twice as easy to lose than to earn) but once you learn, hopefully you'll earn a couple coins here and there.
The other way is to get a job. Online or physical, it's up to you. Use the money that you get to buy bitcoin (or get an employer that pays in bitcoin) and ta-da! You have more bitcoin.