First 2 doses of rabies vaccine hurted but not other ; why? the first 2 hurted some hours later after getting the vaccine but the other 3 didn't; why?

Building resistance: Reports suggest that it is pretty common, more than 50%, to get some pain at the injection site with redness and swelling. It would also be theoretically possible that after the first two doses, you started developing some immunity or resistance to the antigens in the vaccine, and it was less irritating to you. Not hurting after the injections suggest you are reacting normally, building immunity.

You've adapted: Most large volume intramuscular injections hurt, so you have probably gotten used to the pain of the injection by using good coping mechanisms. I would make sure that the vaccine was stored properly and I would also try to determine what happened to the animal that exposed you to rabies. If the animal that bit you is still alive and has no symptoms, you have nothing to worry about.