LOL @ Axelle. Screaming needs no translation indeed.
I was in extreme pain first couple of days after surgery. Ask the nurse for morphine. They should have morphine drip or injection type. If the nurses still don't understand you, show them these phrases;
"คนไข้ปวดมาก ต้องการมอร์ฟีน", "ช่วยดูว่าสวนปัสสาวะกับถุงปัสสาวะปกติหรือไม่"
Translation: "i'm in so much pain, pls give me morphine." and
"Pls check the catheter and urine bag if it's normal."
I'm Thai. If you need any more translation let me know. Get well soon darling.