For me running is more mental than physical. I weigh damn near 300lbs yet I keep forgetting that I am a fat guy.
You can do this! You got this! Don't tell yourself you can't do it or that it is too far.
Tip: I got through my first continuous 20 minutes run by doing a body scan every 5 minutes. I evaluated my pace, breathing, how my muscles fealt etc. I kept telling myself I just made it 5 minutes, what is another 5? I just made it 15 minutes 5 to go...piece of cake!
When you feel weak or lack that drive only focus on positive things. Even if you quit your run early. Look at only the positives.