I had a very similar experience years ago, I tried to start running and I hated it. I went and got a heart rate monitor and found that after I was going for a while where I started to hate it, my heart was up at 180 or so. I started doing alternating run/walks so that I was averaging more like 145, and it was actually enjoyable and I'd get in the zone sometimes. After a while I managed to get up to half marathon distance. I'm a little skeptical about the zone 2 craze that's hit recently, but definitely, if you're just starting out, it's very easy to try to run like the other people you see on the trail and exhaust yourself. A heart rate monitor is very useful to help keep yourself in a reasonable range that's actually enjoyable and sustainable.