Hello, i've been having breathlessness for a few years (mainly when walking uphill/stairs), more recently when talking. what could this be?

Pulmonary or: cardiac disease. This is more than just deconditioning. Please seek medical evaluation.

See below: I would recommend starting your eval with a pulmonologist. You need possibly need a few things done for evaluation. If needed, the pulmonary doc can refer you to a cardiologist. if you need assistance, I would be glad to discuss this with you.