Birth control VS pregnancy symptoms

So, I’m on the pill and I rarely get a period anymore. Lately my nipples have been sore for WEEKS and I’ve been feeling quite nauseous. How can I tell if it’s just my birth control or if I should think it’s early pregnancy without taking the test? Obviously it’s kind of early but I was wondering if there were certain ways to tell if it’s just the pill, eating habits, or if I need to look further into it.