What Causes Stomach Pain And Blood In Stool After Taking Diclofenac Sodium DR?

I suffer from psoriatic arthritis. I also have osteo arthritis in my knees. I have been taking meloxicam for a few years and get some relief from it. A friend advised her doctor prescribed DICLOFENAC SOD DR, 75 MG TAB for the same type of issues & I asked my dr about prescribing to me. He said I could try it, 1 tablet, twice daily. I quit meloxicam & started with this. I have experienced some slight stomach pain & a small amount of bright red blood in my stool. I stopped the diclofenac & went back to meloxicam & paid & blood in stool stopped. Waited a week & went back to diclofenac, only one tablet in the daytime & same symptoms, so I stopped again & went back to meloxocam. I also take 3cc injection of methotrexate once a week. I get great relief from joint pain from diclofenac; is there something I could take with it to protect my stomach or should I give it up?