Xp issue

While doing the story the xp bugged on me and i completed all 6 acts without the xp bar or level increasing. By the time the story was complete to endgame i was level 24. Since completing ive had to go back to the story which was on par with my level and repeat. With doing so i noticed the xp was greatly increased as should have been 1st time round. I am now level 65 and tried to go into maps as a group to gain the xp boost for levels and have done so since level 60. However i seem to be having a very similar issue by not getting the relevant xp i should be getting. I know i should be getting a very considerable amount of xp to what i am due to doing the very same thing with 2 other characters. Can you please help as im at my wits end