This is called menorrhagia
and is very harmful for your body because you may be anemic(weak blood) and for this cause you feel weak.
You should go to the doctor immediately to determine whats are the cause.
You should do at least an ultrasound
to see your uterus
If you have big myoma
,polips and submucosal myoma these can interfere with your desire to be pregnant.
take care of your self