Is it okay to take more than 800mg ibuprofen at a time if menstrual pain is too severe and can't be relieved after taking 800mg tab and heating pad treatment?

Not at the same time. There are other treatments for premenstrual pain- pl ask yuor Gyn. Hope you feel better.

Occasional use of a second ibuprofen 800mg is not going to cause harm, but ask your GYN physician about low dose oral bcp's, which stop ovarian estrogen production, and will control the menstrual pain better. Your physician may suggest taking several packs in a row, without the placebo week, to diminish the number of withdrawal bleeding episodes.