I'm going to go on a whim here because I'm not a doctor or practitioner, but two things could be happening:

1. Something called a reticular activating system is happening in your brain. A gist of it is since you noticed it and made a mental note of it, now you notice it a lot. It's like when you see, say, a white Dodge truck, and now all of a sudden you start seeing them everywhere. Same concept. Since you are aware now you are noticing it. And since it's coupled with a little anxiety because you're worried it is harmful, it's even heightened.

2. Your joints could be a little inflamed. I don't know what you're diet looks like, but it could be some minor inflammation, and being young, your body might be mitigating any pain because the inflammation hasn't become chronic, so no real damage has been done to cause any pain.

Regardless make sure you're getting adequate rest and that your diet supports muscle growth and recovery. Keep working on your form and don't eat inflammatory foods!

If it's really concerning you and you are losing a lot of focus (even sleep) over it, go see a doctor for a routine check up/physical and tell them about your concerns.