Cystitis??

Wow, I haven't been on in long time. Goodness. Well now I'm kinda hopefully back!

So the latest piggy trauma has occurred. Dexter has been peeing large amounts of red-ness. I took him to the vet, she palpated his bladder (he would leap forward squeaking every time she touched his bladder), took x-rays (which showed nothing) and he stayed there for the day to get a urine sample and for observation.
The urine sample didn't have any blood in it (it wasn't red, but I had separated him for a day on a white towel so I know it's him) and there wasn't a high amount of calcium crystals or anything that would signal stones and there wasn't any bacteria or whatever that would tell her that he has a UTI.
She ended up sending him home with Metcam to be given whenever he seems to be in pain (he usually squeaks when he pees). And she diagnosed him with Cystitis, where the lining of his bladder is really sensitive and gets irritated easily causing blood. I gave him the metcam for week and the bleeding/redness/squeaking gradually stopped.

Now, a month or so later he's squeaking and peeing red again. I gave him more Metcam and I'm calling the vet tomorrow, but does anyone have expierence with this sort of thing? Any ideas that might lead to a solution?

Thanks for reading! Sorry it's so long...
I took a picture of it with my phone if that helps at all...