Is this post partum depression or am I just tired?

I am 42 years old and have a two month old baby. I have 3 other children ages 21, 18 and 13. I also have a grandson. I find that little things irritate the stew out of me. I also would rather clean the house or go outside rather than hold my baby when she cries. Of course when I go outside her father brings her out to me because she is crying. I am resentful that it seems everyone wants to hold her and rock her to sleep and when they don't have time or are not here I have to. In the first 2 weeks I would hold her while she ate and put her in the swing and she was fine.