My psvt specifically acts up sometimes after i stretch or after i take in a deep breath, anything that seems to put pressure on my chest cavity. why?

There are many: different forms of SVT so it is difficult to answer with certainty however in general anything that modifies the conduction timing in the heart or the frequency and timing of extra heart beats can trigger an SVT in a susceptible patient. Stretching and deep breathing can modify the physical structure of the heart and thereby the timing by increasing the blood return or trigger extrasystoles.