Pain due to shaving

I consistently get lumps under my arm due to shaving , is what my mother thinks. It has swelled up some but more of like a hard type of swelling. If swells up very little but the lump itself is very hard. The affliction if range from 7 out of 10, i cant really move my arm without pain. I've search around and come to the point where i know it is not an Cysts infection nor a boil as this is the third time i have gotten this, through time it has went away. It has always been in the same spot and under the same underarm. so far this is the longest I've ever had it , 8 days to be exact. Would you happen to know anyways to treat this and stop it from coming?