This is totally normal and since you have had a test to make sure it wasn't an infection it's just a matter of managing this uncomfortableness when going.
Its sounds as though you are on the right track with lots of fluids. I found it really helped to use a peri bottles with warm water and I gently sprayed while going. Silts baths will also help. Don't hold your urine too long out of fear of the pain because that will make it worse.
It took about 2 weeks for my pain to stop completely but everyday it did get a little better. Do try the peribottle it does help. You can also add a bit of baking soda to the warm water as it will neutralize the urine and stop the stinging.
Hope that helps.