What might cause white discharge from only one breast when squeezed?

[mirmelnir]

I'm 28, using Mirena (IUD birth control, for clarity), no periods for about two years. Maybe a month or so ago I noticed a thin, white liquid coming from my right breast when the nipple was squeezed. At first it wasn't much, just a drop or so, but lately when I squeeze my breast a stream (or two, as the case was today) will shoot out.
There's no pain, no blood, and neither I nor my spouse have felt any lumps in the breast. Before this started there was a lump in my armpit, but it had disappeared and we suspect it was a cyst.

I know I should see a doctor but I'm uninsured and recently unemployed. I need to know what signs and symptoms to look out for to determine if it's serious, hormonal, or an infection. Every source I've found leads me to believe it's not life-threatening but they all say "ask a doctor." What would a doctor be looking for?

I'm pretty nervous. Any information will be appreciated, thank you.