Is it permissible to break the fast in Ramadan due to the worsening of ulcerative colitis, which causes diarrhea, bleeding, and abdominal pain, along with the desire to start natural treatment, bearing in mind that I am a breastfeeding mother?

If fasting increases your illness, delays your recovery, or causes you significant harm, then you have a dispensation to break your fast. You must make up the days you missed, as Allah Almighty says: "And whoever is ill or on a journey - then an equal number of other days." The illness that permits breaking the fast is one with which fasting becomes difficult, or if one fears that fasting will worsen it or delay its healing. This is part of the ease of the religion and the removal of hardship.