findthatbook | Middle School Aged Book For Girls

Help please! I'm looking for a book I for the life of me cannot remember the name of. I only remember bits and pieces about the plot, but I think the main character was a young girl named Meghan. She was I think middle school aged and she had missed a month (or more) of school from a sickness (something like mono or something...) and she had an embarrassing incident that had to do with underwear in her class. There was also something else with her making friends with mean, popular girls but I honestly can't remember anything else and it's been driving me crazy! I think it was from sometime between the early and mid 2000s, but it was definitely a chapter book meant for young readers because I must have read this when I was either in elementary or early middle school.