I have a problem
 

When i relax, my back muscles too so they spasm.

And this make me difficult to fall asleep :(

Does that happen in bed only, if you sleep or relax in a recliner does it happen too?
Do you have a good mattress on the bed?

Often the memory foam toppers can help if the mattress is getting old.

Try Somatics by Hanna. It's a book with exercises designed to get rid of spasms and chronic tension in muscles. Interesting stuff.