I've taken Wormwood as a cleanse as well, and it didn't affect my period. I didn't know cayenne and bayberry stop bleeding - in what form do you take them?
The reason you're not bleeding means your hormone levels are low. When the hormone level drops rapidly (PMS), the uterus sheds the endometrium, but after the first day of your period the hormones should start increasing again. Three weeks of bleeding is VERY serious. I'm sorry, but you're out of the realm of herbal healing or stress relief. The only herbs I know that help with hormones are Black Cohosh and Dong Quai - I used to take them together. They also come in creams, but those are rather expensive, though they absorb quite well.
If I were you I would go to a doctor, no matter how much you don't trust them, and get a shot or pills to stop the bleeding. I hate taking pills too, but you could really benefit from birth control here - at least for a few months to let your blood build back up.