Having chest pain?

I am having some uncomfortable pain and soreness in my chest. My mother says it is gas (which doesn't make sense to me). Others say it is a pulled muscle, but I haven't been lifting or doing strenuous exercise at all. I had this same pain around this time last year and it went away about a week or two later. When I lay down on my back, it gets worse. When I lay on my chest or put pressure with a pillow it feels somewhat better. I don't want to go to the doctor unless I absolutely must. Should I wait for 2 weeks and see if goes away like it did last year? Thanks in advance!