A lot of possibilties. If you're young most likely isnt heart attack signs but be cautious just in case. Another possibilty is puberty, especially if you're a female. You could also be sore from exercise you could've possibly done. It could also be anxiety but please don't self diagnose. Those are all the possibilties I can think of, but I'm sure theres more.
I would listen to her. Don't interrupt unless she allows you to. She is very sad at this time and needs someone to tell everything to. Don't say anything that might bring her down. Tell her postive things!
