finished period but cramps ? someone help

Victoria
Finished my period October 1st. Or least I thought I did .... I'm getting cramps and a lower back ache right now like I'm expecting to see it any minute . I feel like it's too soon for ovulation . But I took an ovulation test yesterday and it was already almost positive . The line was pretty dark but not as dark as control line . Anyone ever have this and know what it is ?