started menstruating 2 days after receiving the vaccination. This was also only 3 weeks after my previous menstruation date; The side effects of my menstruation were more severe than normal, heavy cramping and flow- almost felt like contractions squeezing and a subsequent heavy flow for 2 days; headaches; exhaustion; The side effects of my menstruation were more severe than normal, heavy cramping and flow- almost felt like contractions squeezing and a subsequent heavy flow for 2 days; The side effects of my menstruation were more severe than normal, heavy cramping and flow- almost felt like contractions squeezing and a subsequent heavy flow for 2 days; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP). The reporter is the patient.  A 40 year-old female patient received bnt162b2 (BNT162B2), administration date 06May2021 (Batch/Lot number: unknown) at the age of 40 years as dose 2, single for covid-19 immunisation. The patient's relevant medical history and concomitant medications were not reported. Vaccination history included: Bnt162b2 (Dose 1, Single), administration date: 15Apr2021, when the patient was 40 years old, for COVID-19 immunization, reaction(s): "Lower back pain", "Headache", "Irregular menstrual cycle". The following information was reported: MENSTRUATION IRREGULAR (non-serious), outcome "unknown", described as "started menstruating 2 days after receiving the vaccination. This was also only 3 weeks after my previous menstruation date"; DYSMENORRHOEA (non-serious), HEAVY MENSTRUAL BLEEDING (non-serious) all with onset 06May2021, outcome "unknown" and all described as "The side effects of my menstruation were more severe than normal, heavy cramping and flow- almost felt like contractions squeezing and a subsequent heavy flow for 2 days"; CONDITION AGGRAVATED (non-serious), outcome "unknown", described as "The side effects of my menstruation were more severe than normal, heavy cramping and flow- almost felt like contractions squeezing and a subsequent heavy flow for 2 days"; HEADACHE (non-serious), outcome "unknown", described as "headaches"; FATIGUE (non-serious) with onset 06May2021, outcome "unknown", described as "exhaustion". Additional information: Event narrative: I received the Pfizer vaccine first dose 15Apr2021, and 2 hours after injection started menstruating. This was 7 day earlier than my cycle should have started and I have very regular, predictable cycle. I am not on any birth control or medication. The main side effect was lower back pain and headache. My second dose also Pfizer, on 06May2021 - I started menstruating 2 day after receiving the vaccine this was also only 3 weeks after my previous menstruating date the side effect of my menstruation were more heavy flow normal heavy cramping and flow almost felt like contractions squeezing and subsequent heavy flow for 2 days, then it tapered off like a normal period. I also experienced headaches and exhaustion. Since the earlier out of cycle timing and proximity to my vaccine injection it seems they are related.  No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202101601787 Same patient, same product in different dose, partial same event