Possible boil? No 'head', should I go to doc or wait?

So Thursday evening I noticed a sore lump on the back of my shoulder. It's bigger, wider, and more painful now. It's firm under the skin past the edges of the red lump itself, probably about as big around as a quarter. It's tender when I move or my clothes rub on it, especially bra straps, but pretty painful to touch.

I've had to get a couple boils lanced over the years before but my mom thinks I shouldn't go unless there's a head, and I can't really recall if that's been necessary before.

So basically, should I go ahead and go to the doctor or give it a few more days?

30, female, USA, back of shoulder, not sure any other info is pertinent but can include it if so :)