I Noticed A Lump This Evening Under My Arm That

I noticed a lump this evening under my arm that is sore. It was not there a week ago as I check myself twice a month. If it was there this morning it was not sore. It feels like the size of a pea when I press on the area. It is also visually noticeable to myself and my husband. I am unsure whether to go to a clinic asap in the morning, if it's still there, or schedule an appointment with a doctor I trust. I rarely see a doctor except for a yearly physical as I am usually in good health. Any advice is appreciated.