Can a change in PMS symptoms and having sex for the first time cause irregular periods?

Hello Doctor,

I have been getting irregular periods recently. I am 20 years old, 56 kg, weigh 159 cm female, and have had periods since I was a teenager. For the past two years, I have had regular periods of 28 days, and most started on the expected date, while some were early or late only one or two days. My PMS symptoms are cramping, mood swings, and discharging of large amounts of fluid from the vagina. Also, usually during menstruation, I have cramping and mood swings. However, these things recently started to change; my period started three days earlier than the expected date. Not only was the period three days before, which has almost never happened to me before, but I also did not have any PMS symptoms before menstruation but still had extreme cramping during the menstruation. Then, the next period was almost two weeks late. This time, I experienced very few PMS symptoms, and during menstruation, I had the same amount of extreme cramping. Lastly, my period is supposed to start, but it has not started yet, and I feel no cramping. However, I urinate more frequently, and the bottom part of my vagina hurts. It has a stinging sensation. Also, when I urinate or hold my urine, that severe pain becomes more painful. Additionally, the left side of my pelvis feels pressured the pain increases when I lie down. Regarding the fluid that is discharged from my vagina, which I have mentioned above, Usually, that fluid is transparent and white, odorless. It is discharged in large amounts during menstruation. However, during the last couple of weeks, it has become yellow, formed small chunks like smashed tofu, and smells like fish. Instead of discharging lots of that fluid during menstruation, they were released in large amounts two weeks ago, two weeks before the expected period. They were discharged in very large quantities. Then once the expected period date arrived, they are almost not being discharged at all, but it still smells like fish. The duration of menstruation remains the same for five days. When I was in my teens, because my cramping during menstruation was so severe, I had an ultrasound test to check if the excessive pain was due to any secondary causes such as diseases. However, the ultrasound confirmed that I had no such diseases. Although this test was done a few years ago, I am still bringing this up just in case it may help. What could be causing these irregularities in the timing of my period and the change in the fluid in the vagina? I mean, for two whole years, my period and everything stayed relatively constant, then all of a sudden, the PMS symptoms were different, the days were not periodic, and the vaginal discharge changed. I had my first sex a few weeks ago. Could this be the cause? Please help.