Can spotting only be a result of pregnancy or stds? or can it be from stress and other different things that can affect your body physically

Not necessarily... : Definitely not necessarily caused by pregnancy or infections. There are some hormonal problems that can cause irregular vaginal bleeding like thyroid issues and poly cystic ovarian syndrome among others. At certain times stress especially when severe can cause menstrual issues as well. Besides emotional stress, poor diet habits, excessive exercise, just to mention a couple can cause this problem.