It will come ... truly it will.
There's loads and loads of advice, which could go on for pages, but ...
Here is a really useful tip.
Aim to run the second half of your run faster than the first half.
In other words, keep some in the tank. Instead of tiring you out, the first half of your run should be warming you up, and stretching your muscles. Then, at your half way point, instead of feeling shagged, you feel ready to "go for it". It feels odd at first, because you have to really hold back when you start off. But it does feel good to get half way round, and feel as though you can pick up the pace.
And ... here's the punch line ...
Because you are running on slowly warmed up legs, it is more likely that you will be able to go a bit further.
Do you have a runners' sat nav? They're good motivators, cos you know exactly how far you're done, even if you change the route. You can get a Garmin Forerunner 205 for about £80 online. You can change your route, but tell yourself ... "I'm going to run just 400m further than last time".
Oh, one more thing.
Don't try to stretch your distance until the distance you are doing now is feeling a bit easy. That way, going a bit further will feel like a natural progression, rather than a big effort.