You’re optimizing your beach bod, but this may represent a local irritant on your chest. Those little hair follicles on your chest that you’re pulling with your shaver inadvertently can lead to some significant irritation around the hair follicles.
I’d recommend starting with a 1% hydrocortisone, which you can find over the counter, and using that after you shave to decrease inflammation. If that doesn’t work, there may be a bacterial folliculitis, in which case I’d recommend seeing a board-certified dermatologist for further treatment.