Could I still get BFP after 14 dpo?

I'm due my period today and done a clearblue digital test - BFN. My ies have been sore, heavy and veiny for just over a week now. They even hurt when I walk. I keep peeing and have bouts of nausea throughout the day. Strangely I have noticed a very prominent brown line from the top of my tum to my pelvis. I have been using the fertillity monitor so know I ovulated and I also track my cervical mucus. I have been getting twinges in my abdomen for the last couple of days. Not sure if it's period or implantation. Thank you for your help. BTW I'm 41 and am TTC. (2nd month of trying and not first baby...son 21 daughter 15)