Have a question please help

I have been ttc for about 7 months now never had problems with my period always on time but since I’ve been ttc my periods have been a day late sometimes I miss it then like a few days after I missed it I come on, can anyone help with this it’s annoying me as I keep thinking I’m pregnant each month but get a bfn Cos I’ve never had problems with my period only since I’ve been ttc

Thank you