Implantation or AF

Amy
Please could someone help with some advise I'm not complete sure but I think I'm about 12 DPO I had light period like cramps this morning and today on and off, I had a big dip in my BBT when I woke, my breasts are sore not really sore but tender! I really hope it's not my period but I have been trying for so long I'm loosing hope!
No other symptoms like implantation bleeding or anything yet! Could some give me any advice to what they honestly think it is, I'm due on next week if it's on time!! 
Thanks in advance X