Not adding up

Been using Glow to NOT conceive for quite some time but this month we decided to see what happens. Well I am needing some help because I just noticed what I think was IB, dark red and also some pink on the toilet tissue. But we only BD'd once during fertile period and once right before. I don't think enough time has passed for IB to be happening based on second time- could the first time, outside fertile window- be what did it? I have really bad cramps since last Friday and again today. Could Glow's fertile window be wrong? I don't know when I ovulated. I have very regular 25 day cycles and don't expect AF until Oct. 4.