Positive to a negative to a positive??

Has anyone had this happen to where you get a positive? Then a negative.. then another positive? On 11 DPO I got this faint positive (first picture). On DPO 12 and 13 I tested FMU and late after noon and got negatives. Then this morning on 14 DPO I got the bottom test on the second photo. Another faint positive. Anyone have experience with this?