Interstial cystitus

H
I have never been diagnosed with interstial cystitus but I have all the signs. I had my water sample sent away but it came back negative. 
I'm in a lots of discomfort. Can't stop peeing and the pressure is quite bad. Don't know what to do. My GP gave me oxybutynin which helps some times, but it's isn't doing anything at the minute and it's meant to help the spasms. Does any one else have it and have any advise how to ease the flare up ? The only thing I can think of that started it was my high protein diet and that I was constipated for a few days. Thanks