Any reasons?

Let’s start with ive had the iud for the past 2 years, i’ve got another year left.

i have gotten a period every month since i got it.

this month, before my period was due, kind of dizzy, getting nauseous on and off all day, and being very tired.

my period is now 3 days late, last night i’ve had mild cramps and some pink spotting and thick discharge (clear)

because of feeling off i took a pregnancy test, the day before my period was due and negative. a day after my period was due took another and negative.

still feeling the same so if pregnancy is ruled out, what could it be?