When you breathe in, your blood, with the help of your alveoli, becomes oxygen (O2) rich and carries this oxygen to your body’s tissues. That O2 is then used and there is a carbon dioxide (CO2) build up, which the blood carries back to the lungs. You then breathe out that CO2. The breathing rate is dependent on the concentration of CO2 in your blood.
So, the more CO2 build up there is, the more you will breathe. Moreover, a higher acidity level in your blood can increase the breathing rate too. This can give you a sensation of shortness of breath and difficulty breathing. The reasons for the higher acid and CO2 levels can vary vastly and need to be assessed by your physician.