What could be wrong? Could I be anaemic?

Hi. Basically, for about the last 5 weeks or so, I’ve had constipation on and off, and I’ve also had some heartburn and abdominal pain. After a couple of weeks my ribs also started aching and my back, and my chest. Yeah, pretty much everywhere, but on and off, and only faintly, and always in different places. I also had my first period about 4 months ago, and have had none since. I went to a doctor about a week and a half ago to check it out, and make sure there was nothing bad going on, and she said she was sure I didn’t have any kind of terrible illness. She said that I was just having a hard time, (GCSEs and some changes at home) and my body was responding in its own way. She recommended some Hi-Fibre gel, which is natural, and I started using it a couple of days ago. There have seemed to be a few improvements in regularity, I guess. But my stomach still feels a bit bad. Also, I’ve been feeling more tired than normal at less exertion, and been getting headaches a lot in the last few days, though school just started. If this doesn’t go away, I don’t know if I can deal with a full week of school, let alone a term. I just don’t know what to think about it all. The doctor also said to monitor my weight, as it could be a sign that I’m anaemic. The tiredness also figures, although I didn’t think to mention it to her at the time. What do you think? Also, what does being anaemic construe, just so I can be prepared in case, and deal with it better? Thank you.. xx