Running motivation anyone?

I started running back in January with Couch to 5K and am signed up for my first 5K this coming Saturday. Yay! But lately, I have felt down about my runs and have thought about quitting altogether. I'm a little dismayed that after four months, I'm still "only" running a 14-minute or 15-minute mile, depending on the day, and don't know if that's normal or if I'm too slow. It's been really humid a lot where I live, and when I get out in the heat, I tend to have to take walk breaks more because I can't handle going full-out when it's 75 degrees at 10 a.m. and the dew point is oppressive. I know I can't make excuses and the running has to get done, but even though I still get out there, I feel dreadful every time I have a run scheduled when the humidity is creeping up. I signed up for a half marathon in October and am questioning if I have the stamina to be outside in July and August doing five, six, seven miles a day. And more.

Do any runners have advice to gain more confidence? Did anyone ever feel like they kind of sucked at running for a while before it got better? I came back yesterday after a three-mile run turned into a walk, and I was upset because after four months, I don't feel I'm a "good" runner and maybe it's not for me. How long did it take you before you felt confident?

I don't really want to quit running. A lot of my family members are runners and I see what it's done for them, especially my dad, who's lost a lot of weight and quit smoking as a result, and is now training for his first full marathon. I would like to sign up for another two 5Ks and a 10K in the fall, but I worry I won't be able to handle the summer training. Since I don't have a full-time job, I have no option for the treadmill if it gets too hot to the point where it's not safe.

What should I do?