Thanks for the query,
Menstrual cycle ranging from 21-37 days is considered to be normal.
Duration of bleeding from 1-7 days is normal.
So you need not worry since you have perfect menstrual cycle.
contact a infertility
specialist for infertility work up which includes
FSH , LH levels,
t3, t4, tsh
other endocrinal abnormalities.
hope this helps,