Thank you for reaching out. 

We are sorry to hear of your painful situation and recommend getting checked out by your doctor if your cramps are interfering with your daily life. You can learn more about period pain and possible treatments here.

If you are bedridden from the cramps, you may daven while sitting or lying down. If needed, even Shmoneh Esrei can be said sitting if it is too painful to stand. You may shorten the davening if you are having a hard time focusing because of the pain. (Minimally, berachot, Shema and Shmoneh Esrei. If possible, add in Baruch She'amar, Ashrei, and Yishtabach.) 

Please feel free to get back to us with any further questions. 

Refuah shlaimah!