Something is wrong! Just two weeks into Aikido and you're doing breakfalls on the side? I'd hate to be in your shoes. At our dojo, we are taught to constantly improve on our forward and back rolls.
Ask your sensei what are you doing wrong before you injure yourself to the point where you have to take time-off to heal.
You have to take your time, maybe learn slowly but more importantly, safely.
I havent brought it up becuase frankly it's gone soon enough. I practice at 6pm, and at 8am it hurts, and the next morning it's all gone. And we're doing tons of forward and backrolls too!