In Phoenix, we call them "Vincas", because they used to be classified as "Vinca rosea". The present botanical name is Catharanthus roseus. A rarer common name is Madagascar Periwinkle.
They are very popular summer bedding here in the low desert because they actually like the blasting sun and baking heat we have from May through September. As a houseplant in Pennsylvania, I would give it as much direct sun and warmth as possible, and let the top 1/2 inch of soil dry before watering again. Yours also looks like it is short of nitrogen, so a low phosphate food designed for tropical plants is probably appropriate.