Feeling Tired, Unable To Concentrate, Eating Less. Pain In Right Chest, Shoulders, Back. Reason?

Hi, I'm a 26 year old male. In good shape and remain physically active. For the past 4-5 days or so, my body just hasn't felt normal. I'd be tired, not able to concentrate, and just didn't feel "all there". I started to think it was because I wasn't eating much...I had taken a few days pretty lightly and should've been eating more. The past couple days I have gotta my diet back on track though. Today, I woke up and had pain on the upper right side of my chest. Sometimes it was just pain, sometimes it would actually throb a little. I also had pain on my right shoulder and right side of my back early in the day. I woke up with some sniffles as well and haven't gotten the most sleep the past couple days...not because of pain...just me staying up to late. I'm a little nervous about the pain in my chest and my shoulder/back area. Any chance you could help explain what's going on?