Lump in armpit

Hi,

I didn't know whether to post or not. I've been noticing over the  past few months that my glands under my armpit have been swollen, no lump. I went to the doctors and they gave me antibiotics, they said if it doesn't go away to come back. Over the last few days I was stretching and was feeling my armpit as it was aching and felt a hard lump. I feel like it has been hurting ever since (don't know if it is because I'm thinking about it more) The lump can be felt most the time but not as clear other times and is very small, which makes me think is it a lump? Don't know if I'm being very paranoid and shouldn't worry, and should see if it goes away. With the circumstances at the moment I don't know if I would even be referred. Any advice would be appreciated:)