Can I do a keratin treatment to my hair after 3 months of hair transplant?

It is best to contact your doctor about post operative care and instructions since each doctor has a different regimen.  In general you can do anything at your stage. 

your can retuen to your normal routine after you are healed. You can do keratin treatment after three months. 

The use of keratin fibers is fine to use after a hair transplant once the crusts are off. I am not sure what type of keratin treatment you are referring to