Felt something similar when I started running. It was runner’s knee. Fixed it by not stopping running and stretching a lot, theragunning and doing strength workouts. Also, knee specific exercises like sissy squats and a lot of mobility exercises. If it happened without you increasing the miles per week rapidly though I would assume it’s something different. Good luck!
Discussion
(Also not trained in medicine so going to the doctor is probably the better idea)
I've been running for about a year and a half. The only thing different is I went on two long hikes in a two week period that included walking up and down 1000+ large steps each time. But again the next day after doing these I felt fine with zero pain. The people I went with had leg issues the next day. I felt great and ran as I normally would have without issue. Then a week later the knee issues started.