Why???

Question.....So why am i so fatigued the days after my period? i will have it for 5 days and then just feel so exhausted for the next 2 weeks and then boom the next cycle of PMS starts all over again. do anyone have any thoughts or ideas to get out of this viscous cycle. Im taking multivitamins, Vitamin D, and trying to eat healthy. Exercise is such a challenge when i feel like this 🙄