Faint test on period

I am 12 days past ovulation and currently on period, but have been getting faint lines on tests for the past 3 days. What is going on?! Chemical pregnancy that just takes awhile to go down? Anyone had a similar experience? I had a miscarriage last month where I tested 10 days past ovulation and my period had started; negative. The next week my period hasn't ended so I tested again thinking that was weird and I had a blazing positive. So strange.