positive tests last night and negative this morning?

I took two tests last night and they were both positive, fairly faint but still able to clearly see it without squinting. I had 3 people also check and they all saw it too. then I take two this morning and they’re negative, like stark white. i’m a little upset and confused.

Last week I had pretty mild cramping that felt like my period was coming but it never showed (i’m on birth control and haven’t had a period for over 2 years) I spotted for like half a day on Sunday, positive tests on Monday night and now Negative:(

i’m assuming i’m not pregnant since the tests were negative with my FMU, the tests all came out of the same box. i plan to take another one later