you did it your self ? you have not fitted the rear wheel properly ... it must be free flow... In worst case you will need to put a a washer on the side where the nut is tightened along with spacer to give saome room to bearing so that the can move freely ....
one more thing check if the bearing were proply dunked in the bearing groove ho sakta hai wo pori tran ander na hon ya new hain tu apny groove say koi aik bearing thora bahir ho jo nut tight kerny per sath lag jata ho .. ..