Can I use back rogaine to get hair back?

You must continue using Rogaine as directed. If you stop using Rogaine the hairs you gained will fall out over time (as you have noticed).  If you restart Rogaine, new hairs may grow but it generally does not regrow all the hairs you have lost.

You may be able to get your hair back with restarting Rogaine.  You have to know that the process of hair loss is gradual and not everyone can gain the same hair they had by restarting Rogaine. 

When new hair grows on stimulus from Minoxidil (Rogaine), it becomes dependent upon the drug. When you stop it, because of the dependency, the hair is often lost. You are try, of course, restarting it, in the hope that the hair comes back, and it might. Until you try it, you won's know.