I'm so sorry you're hurting. No other outbreak will hurt this badly, I promise.
You don't say if you're male or female, so I don't know if going to the bathroom hurts because you have sores on your vulva and the urine is hitting those sores, or because you have sores inside your urethra. Both are super painful, but drinking water will help in both cases. It helps dilute the acid in your urine which is why it hurts so much.
If you are female, you can also get one of those squirty water bottles and squirt water on your vulva as you urinate, or get some latex gloves (you can get these at any drug store) and cover your vulva with your hand as you urinate.
For external sores only, you can try a numbing spray, like Dermoplast (make sure to get the one without antibiotics in it), or anything that ends in 'caine - Solarcaine, etc. You can also call your doctor and ask for a prescription for lidocaine ointment, but that doesn't help the sores dry out.
Try ice packs, too, or bags of frozen peas, which mold to the body better than a lot of ice packs. (Hint - the vegetable matters - green beans poke and hurt.)
You can use tea tree oil on the sores to help them dry out faster, but DILUTE THIS. Wet a cotton ball, then add just a couple of drops of tea tree oil to the cotton ball. If you don't, it will make your crotch BURN LIKE FIRE. It may still burn, but have an ice pack ready for after. It takes some getting used to, and the smell is awful, but it can really help.
Let the air get to your sores as much as you can. Sit in front of a fan with no underwear on, or just go without bottoms when you can. (I know this isn't always possible.)
Stay on top of your meds. Take exactly as directed. It will help. What did they give you? What's the dose?
It may take a few days, but you WILL feel better, and it won't ever feel this bad again.