Faint line

So about 5 days ago I took this test. I took the test and stupidly waited only the minimum two minutes for results because I was running late to work. I saw nothing come up after two minutes then left. When I came back home and started cleaning up I picked it up off the floor and looked again and saw this faint line. The next day I got my period however my flow was just a tad lighter than normal and it only lasted 3 days (my norm is 5 days). When I stopped bleeding the last day I took another test and it came back negative but today I've been experiencing back aches and cramps and nausea and spotting. What does this mean?