armpit bump hasn’t gone away

I’ve had an bump in my right armpit since November or December. I went to the doctor in January and she said it’s nothing to worry about. It’s currently May, so it’s been about 6 months since I’ve had this, and it hasn’t gone away. It legit hasn’t changed in size and it doesn’t hurt. I’m going to go back to the doctor this week because I’m worried. What do you guys think this can be?