Faint positive AFTER a period??

I'm baffled. I just had a week long period, with moderate bleeding the first three days and spotting the last four days. I'd been testing like crazy before my period and hadn't gotten even the faintest shadow. Last night I tested just for the fun of it (hello addict!!) and I swore I saw a faint shadow, but it also could have been a nail print on these cheapie tests. I took this test this morning with second urine and there's a faint positive, but it just doesn't make sense!! Could this be just an evap? It was within the first 5 mins though. 
I've been pregnant three times before but the first pregnancy was ectopic, and now I'm scared something weird like this is another ectopic! Thoughts? Anyone ever had a bfp after their period and have it be so light like this? My live birth's bfp' were soooo strong and dark! Maybe the period was a missed miscarriage?
The only pregnancy symptom I have is some mild acne and slightly sore nipples, but nothing like my previous pregnancies!