Im level 38 in 58 areas and not getting barely any exp ? Please help!

I've tried solo play and playing with a friend its making no difference the exp rate im getting has just dropped a very significant amount when I reached 36 in cruel difficulty act 1 as I just got to the cemetary part. Ive played through all act 1 cruel and act 2 cruel and only got 2 levels and now moving on with act 3 cruel. This just doesnt seem right it definitely has just capped my exp rate somehow is this normal ? Should I go back to lower level areas to level up normally again ? If you know anything please help! Thankyou