Emotional Wreck

We have been trying to conceive for about six months now. Have been married for a year in a half charting cycle and trying to conceive naturally.  I am 30 years old and my husband is 34. Yesterday I went to visit my mom and spent the day with her to come find out my little sister is expecting! I am on a roller coaster ride of emotions. Even though I'm happy for her it's hard to understand how without even trying or wanting this baby things just happen so easily for some. I'm trying to be positive but it's sooo hard. I came home crying last night. The only thing my mom wants to talk about now is the baby on the way... I guess I will be tortured for the rest of the months up until birth. I don't know how to deal with this situation. Has this ever happened to someone?