Slow down. Most people who feel stuck at a certain level of running are simply running too many of their runs too fast.
Try this thought experiment: Let’s say you want to tack on an additional 15 minutes to most of your daily runs. Would you be able to do so by doing your normal run and then sprinting for 15 minutes? No. Would you be able to do so by doing your normal run and then walking for 15 minutes? Of course. Would you be able to do so by doing your normal run and then continuing on at that pace for 15 minutes? Probably, but it would be difficult, and if you tried to do it every time you ran, you’d either start to be unable to hold the pace or you wouldn’t even try because every run would have become too much of a challenge. So the right pace in this scenario is somewhere between a walk and a little slower than your current normal pace.
Apply that thinking to your running as a whole when you want to run more. If you want to run more on each run, run at least the first half of the run slower than you do now. If you want to run more days per week, run each day a little slower than you have been when running fewer days per week.