There aren't meds to treat gender dysphoria, and each trans person's level of dysphoria and their ability to live with it varies a lot.
At any rate, every individual's transition experience tends to be a bit different. The author's seems to be a bit atypical, in that she felt good immediately after the surgery and then started feeling the effects later. Usually the most intense pain is in the first 3-5 days after the surgery.
It also varies a lot by a person's pain tolerance, just as with any major surgery. In my case, I was on a morphine drip while in the hospital for 3 days, and then just on extra-strength Tylenol for a couple weeks.
I suspect in the next chapter we'll learn that there was some complication that led to the current pain.