Period & Pregnancy

Hey everyone. I am 30 years old and for the last month in a half I've been feeling weird (extra headaches, mild cramping, lower back pain, nausea, more tired and cranky) I had a period in july for 4 days (it stayed an extra day, my period is normally 3 days) then in August it only was on for a day an a half. This month is kinda different (I had light pink spotting for 2 days, 2 regular red days and 2 days of pink spotting again). I have taken over the last month I have taken 3 dollar tree pregnancy test and a rapid first response and they came back positive, I took a first response a week later and it was negative, I went to the dr to get blood work done and that was negative (they tested hcg levels not hcg hormone levels, apparently there is a difference, this month I took 2 dollar tree ones and they were positive and also a clearblue test which was negative. If I'm not pregnant what would be the cause of test to be positive?

With my oldest daughter I found out when I was 7 months pregnant, that I was pregnant with her. I had a period every month for 7 months.

Could this what is going on now?

Thanks