5 months is when both of my kids got their first teeth. It could be teething. Wouldn't hurt to check with the pediatrician to make sure something else isn't going on, though.
I think she may be teething. my baby has been teething since 2 months and at first I didn't know what to do. I asked his doctor was it possible for him to be teething at this age and she said yes "he can teethed for several months before cutting a tooth!" This was surprising for me. Rubbing his gums,or putting a damp towel in the freezer worked for him.