Help with Senna Tea!!?

About 3 weeks ago, I bought Senna Tea (Herbal Medicinals Brand) thinking it was somewhat of just a digestive aid, and it was safe to drink two large tumblers of it daily. I was not constipated at the time. Anyways, I drank two large tumblers, had awful cramping, and horrible diarrhea but I was okay. I just returned home from a Fraternity Formal and feel very constipated (not easy to relax and use the restroom when there are so many people around) I would like to take the senna, but have heard horror stories of your body getting used to it with prolonged use, and you need it to go to the bathroom as a result. Well, i do not want to mess up my bowels, so I was wondering if its okay to drink it 3 weeks since the last time. i will not get addicted correct? i have not had it since the last time which was 3-4 weeks ago. thanks!