is my milk going away in one boob?

i have a 3 week old and lately she’s been sleeping on my chest a lot, specifically on my right boob and she did it for 3/4 days straight. It started to feel really sore as the time passed and when i would pump I would only get two ounces but before I would get 4. My left boob is still making the same amount of milk as before so i feel like somethings wrong. also i can still feel when i have a let down but my boob doesn’t seem to get full, it just stays soft but my left boob starts to feel more heavier like it did beforez