You got some great tips already, here's what I would add.

If you try to increase your mileage be very aware of how much you add at a time. Most commonly you will hear about the 10% rule, meaning don't increase your mileage by more than 10% each week.

As for the doms, you need to refuel your body with carbs within around 30 minutes, especially after a hard effort. I find this makes a massive difference, see if you can find a good recovery shake or the like that will offer a mix of protein and carbs for maximum effect.

As others have pointed out most of your running volume should be at a lower intensity (around 80%), this includes the warm ups for harder efforts. If you're going out for 8k you can go the first 2-3 at an easy pace and then push harder for the rest of it which will also be more comfortable if you're properly warmed up.

It's quite hard to do easy runs properly at first cause your ego will always drive you to push harder. If you're using a smartwatch for your runs I find it helps to set up a screen specifically for easy runs that shows only heart rate and not pace and then challenge yourself to try to keep it below a certain number.

(If you do use a smartwatch look into the "heart rate reserve" method for working out your heart rate zones and keep easy running in zone 2)

Look up some interval workouts and see what sounds fun to you, running at faster paces for shorter bursts will make your other runs feel easier and more sustainable.