Vomiting blood is an uncommon condition but has many potential serious health problems. So what is the main cause of vomiting coffee grounds-like blood?

Since the 3rd day of Tet, I have had diarrhea every day but only once a day, some days early in the morning without eating or drinking anything, I have had diarrhea 3-4 times in a row. I always feel like I want to go but my stomach doesn't hurt, along with frequent urination, painful urination and a little blood for 3 days. Currently, I only have frequent urination and a little painful urination about 20%, I still have diarrhea. I feel very uncomfortable. So, doctor, can you tell me what causes prolonged diarrhea and frequent urination? Thank you, doctor.