Talk to your doctor. They might be able to either prescribe a different type of allergy medication that your body hates less, or give you prescription-strength laxatives.

While you wait for your doctor's appointment, try a high-fiber diet with lots of fluids. The last thing you need right now is a tear in your colon or rectum.

Sounds like you were getting ready for the Mother of All Snee-Sharts! (Aka, shnart.)

A bloody, crappy bit of business you got...get ye to a doctor.

They make OTC stuff to help. Why are you intentionally torturing yourself by withholding those? Is this some kind of masochistic scheme you hatched but now regret? No sympathy from me. You dug your own hole (get those fingers in there!)