It's not uncommon at all.
When you do get back in the pool, try to get belly down in the shallow end. In a horizontal position the regulator will breathe more naturally. See if you can just lay down there breathing for 15 minutes watching your fingers wrinkle. Don't rush this phase because it will pay off down the road. The mask clear skill may challenge you in a similar way and there are similar ways around that if it proves to be a problem.
Pete
I start everyone standing up in teh shallow end and breathing above the surface through the reg. We even try coughing through it, so we get comfortable. Then we go to laying face down in the shallow end, bobbing on the surface, breathing...... And counting - in 1,2,3,4 and out 1,2,3,4.......
You may also check to see if your rental/school regulator has a venturi control or flow rate control knob. You amy want to open it so it releases air more easily....