Cramps and Femara / letrozole

Hello ladies,

This is my first cycle taking Femara 2.5 and I'm kind of confused. Today is my 14dpo and i been cramping almost all day felt nauseous this morning. I keep feeling like af is around the corner light back pains and mild front cramps but still nothing. I usually get AF right in the morning no later then 10am always but this month it isn't coming. I keep going to tbe bathroom but no show. I dont think I'm prego because i had a bfn at 11dpo so I'm not expecting to be pregnant. My question is has this happen to anyone else. Does Femara change you cycles. I'm confused.