What’s most likely to be going on?

I’ve been feeling really hormonal and emotional lately, more than usual, these past three months and I missed my period this month.

I haven’t been sexually active since October, I was mostly on birth control and I tested negative to pregnancy in the first few weeks.

I’ve had what I assumed must be periods, for the past three months since having been sexually active.
I can’t be pregnant, can I? Or going through premature menopause?

What’s most likely to be going on?
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