Is it normal to have irregular periods after taking birth control pills?

Patient's question:

Patient Information: Female, 22 years old
Medical History (Onset time, main symptoms, etc.): I have always experienced heavy menstrual bleeding, and my lower abdomen has been in pain for about 6 hours on the first day of my period. Before my period starts, my left chest also hurts. This has been going on for 4 years. However, after taking a birth control pill at the end of October, my menstrual bleeding in November was very light, and my lower abdomen didn’t hurt anymore. This month, in December, my menstrual bleeding is even lighter—only on the second and third days, and it’s the same as when I used to have it on the fifth day. There were no warning signs before this period. A pregnancy test showed I’m not pregnant. I’m seeking help from all my friends—is this normal? Should I see a doctor and take medication to regulate it?
Past Treatment History and Allergies/Genealogy: None. It has always been normal before.

Doctor's answer:

This situation is likely caused by birth control pills leading to menstrual disorders. There is no need to worry, as the menstrual cycle usually returns to normal within 2-3 months after stopping the medication. Birth control pills should not be used more than three times within a year, and only once per month. Gynecological diseases are a common condition that can easily occur. During treatment, women need to pay attention to self-care, especially in terms of hygiene. It is recommended that patients avoid sexual activity during treatment and maintain good hygiene. Finally, we wish female patients a speedy recovery.