Can amox clav 875 irritate my gastritis to the point where i feel lightheaded, short of breath and bad cough?

Treatment or disease: You may be confusing the treatment with the symptoms of the disease.

Maybe: Augmentin's main adverse effect is gastrointestinal distress, so yes, it could exacerbate symptoms of your gastritis; however, shortness of breath and cough are all respiratory issues, so i would not necessarily attribute these to the augmentin (amoxicillin and clavulanate).