2000 SAAB 9-5 Overheating/reservoir backing up

Engine Cooling problem
2000 Saab 9-5 6 cyl Front Wheel Drive Automatic

I was driving my car and the hazard light popped up, my car was way way hot. I pulled over and let it cool off. I am not knowledgeable when it comes to my car malfunctioning in any way. I did not let it overheat, I pulled over before it did. I sat waiting for my road side assistance to get a tow truck for me, almost 2 hours later I decided to drive it home carefully watching the temp meter. It go a little warm but kicked right back down to where it normally is. The rest of the ride home (12 1/2 miles) the temp was fine. I got into my drive way and let it run to see if it would get hot or over heat again. It did not. So, I thought wishfully that it was just a fluke and all was well again. I get in the car to drive to work (7 miles) with a watchful eye on my temp gauge. Almost there, about another mile or so to go, the temp starts to go up again. I pull over let it cool off and continue towards work once cool. I get out of work my coolant is low so I put some distilled water in, and drive home (7 miles). Almost home, the car begins to get warm again, not too much but a bit warmer than normal. I make it home with out cause to pull over. I get home and have my boyfriend take a look at it. He knows little about cooling systems as well as myself, so we decide to look on the internet for answers. Most all of the answers we got were to flush the system. So we get instructions and he flushes it. About 6 months ago I had put radiator stop leak in because I was losing a lot of coolant and did not know what else to do until I could get it fixed. It turned out to be a bad hose that got replaced, but a lot of the gunk from that came out during the flush. We filled it with distilled water (no antifreeze because I am out and can not drive to a store to get any as of yet) and let it run. After a while, 15 minutes, it begins to get warmer than normal again. With the hood popped open, we look to see if we can see any leaks or anything at all that will clue us in to know what is wrong. Water begins leaking from the cap on the reservoir. I did not allow it to overheat, so I don't know if it would have turned into a full spray from the cap or if it would stay the consistent leak that it was. We did not see any other leaks. Could someone PLEASE help me? I'm lost and worried.

Thank you to anyone that can try to help me.