I took a week and half off running for runners knee and it feels like I’m back where I started

I started running 8 weeks ago. I was having some dull aches in my right knee and because I stand all day for my job I decided to take some time off running and just weight lift and do some stretches with my quads and hips to make it better. I just finished my third run in a week and I can’t keep distance at all. What was my easy 12:30 mile now feels like a tempo run. My heart rate was like a 170 at one point. I have been weight lifting 2-3 times a week since January so I always have some level of fitness but I’m so frustrated. I thought by now I would be able to do my normal 2-3 miles but after 1 mile I’m exhausted. I am in the Deep South so heat and humidity do affect my runs but I’ve been running all summer so idk. It was 75° today with 93% humidity if that matters.