I can not stop spotting :( so worried

Hello! I'm 26 and II have been spotting for more than 3 weeks now... It all started in April when I should've gotten my period but I didn't, neither did I get it in May and June, in those months I had light brown spotting/discharge for like a week and then that's it, my period came in July and lasted for 11 days, and then a week and a half after I started spotting brown again and it has not stopped!!! 5 days ago I woke up and I had bled a lot on my underwear and yesterday I had sex and the same thing happened. I have an appointment with a gynecologist next week but I am so scared, I also have lower back pain almost every day and it is driving me crazy, I keep thinking I have cancer 😭😭😭