Well, if you can run 5k, you clearly can run for toffee 
.
What's your training plan? Just "more" is not enough for some of us. You might want to include some speed training and/or some hills, some distance, and some recovery. The speed, hills & recovery make the distance come easier.
Speed = intervals where you run as fast as you can for a certain distance (e.g. 200m / 3 lamp posts / to the end of the road), then slow down to recover, then do it again, and again, and again.
Hills = run up a hill as fast as you can; go back to the bottom, recover & do it again, and again, and again.
Distance = do a longer run every week (this is your 5k - your other runs can be shorter), and each week add a bit on (e.g. one or half a km each week - if you're aiming to do a 10k race in June, you should be doing 12k or more in your distance training runs by then; 16 weeks from now, adding half a km per week, would easily do that).
Recovery = run slower than you want to, work the lactic acid out of your muscles, and just enjoy it without worrying about your performance.
How are you tracking progress? I didn't think I was making any progress at all when I was using a phone app, then I got my Garmin. After 2 weeks I could see I was getting better - literally a few seconds off my times, every single run, so not massive but steady & clear progress. That was a massive motivation boost. As are new running shoes, there are some great deals in the sales at the moment.