Start Zoloft, 2w later add pristiq (desvenlafaxine). 3w later stopped both & on Prozac for 1w now. Worsening shortness of breath, can't fill lungs completely. Normal?

Consider ALL causes. First consider ALL possible causes of shortness of breath – including asthma, pulmonary thromboembolism, cardiac arrhythmia (including that triggered by a new Rx) SSRIs are not likely to cause shortness of breath, but almost always cause yawning, sometimes severe.