Mastitis? OR - ?

[LomahAcres]

Pixie is a 4 year-old mini-Nubian, born and raised in my herd. Previously milked through 2 freshening, dried off January. She was 'supposed' to be bred to my Kinder buck for April kids (due date would have been April 15th), but I did not see the breeding, and a few weeks later she looked to be in heat again. I did some pregnancy tests in Feb. on a few other does, I thought I would do Pixie too, but when I pulled her out of the group she was obviously in heat, so I skipped her. I have been keeping track now and she is having heats about every 18/19 days.

This past week, I noticed one side of her udder is larger - like she is filling up with milk? I felt her over and she is not hot or hard, and I was able to squirt some out. But it's only on one side - the other side is dried up like normal. In her past freshenings she has been nice and round and even. Could she have mastitis? Would it be on the filling up side, or the dry side? Is there something else that could cause her to come into milk?

I really don't know what to do next to find out what this is? Pregnancy test? Mastitis test? Milk her? Leave her be? She is otherwise normal, eating energetic etc.

Any thoughts, opinions, advice, appreciated.
Thanks
~ Kristen