It is not true at all that you cannot pray for this
period of time. You just need to repent before the Almighty and request him to
forgive you. It is not the sin which matters so much before God as the attitude
one should adopt after it. So invoke His blessings through prayers and
supplications as soon as you can.
Unfortunately, some Muslim teachers and preachers are very
harsh and stern in such matters. They should realize that such an attitude is
counterproductive to their aims. Please just read a good translation of the
Qur’ān and ignore such harshness as much as you can. Do remember that the
harshness you bear will be a source of reward for you by the Almighty.