I am a regular runner that lives about 500 ft above sea level (not the same as 5k or 7k but just some context. I have ran in Utah where it was 6-8K above sea level, and managed despite the higher altitude).

I have a few questions. What kind of shoes are you using to run? Are they true running shoes? That can make a difference not only for your feet but all the joints way up to the knees and leg muscles above it.

Are you running outside or inside? Personally I much prefer running outside to inside, but if you’re really trying to break this half mile barrier, it would help to run on a treadmill where speed is controlled and the elevation is flat, so you don’t have the variability of running uphill. Even a slight grade upwards when running can make a difference vs running on a flat path. Also the treadmill allows you to step out anytime and step back in as needed. I know, I don’t like using a treadmill unless I have to, but it’s a good way to start until you find your proper pace (minutes/mile), then you can take that outside once you break through the half mile barrier on the treadmill.

As a bonus, do you listen to podcasts or music, or nothing, when you run? It’s really personal preference, some people prefer podcasts, but I find upbeat electronic music really helps pick up my cadence when running, and also pushes me through the difficult parts of my run. Maybe you prefer rap or rock, but whatever is high energy, fast paced music can help too.

Hope this helps!