Pregnant and lump under my left armpit

I’m 13wks pregnant first time mum and about 9/10wks ago I found I lump in my left armpit. Saw the doctor and he said your pregnant what do you expect not helpful at all. I’m concerned as it’s still there and feels a bit bigger and is painful at times. I’m going back to see a different doctor today and would like to know what the doctor should do, other than feel my lump. I’ve not ever herd of anyone getting lumps in the armpit cos of being pregnant. I’m a first time mum to be and getting more concerned about my lump by the day. Any help and support would be a great help. Thank you.