My wife doesn't want to have sex

My wife and I have a great relationship except for our sex lives. We are pretty transparent and honest, and basically, she feels bad because she never wants to have sex. She doesn't have the desire. She's also never orgasmed. She feels like a terrible wife and fears I'll cheat on her. She doesn't know why. Last time we had sex, she cried and felt bad and didn't know why she cried. However, she also told me that the last time we had sex, she felt me in her, but it just felt "ehh" and wanted to stop. That makes me feel really awful. We rarely have foreplay. Everything I try tickles her, so she makes me stop. We are both frustrated but very much in love. She and I are in our early 20s. We're married and we have a baby on the way.