When a doctor asks "is there any chance you could be pregnant?" What exactly do they want to know? I mean just by having sex there is a chance, however small, that I could be pregnant at any given moment. I take birth control so I seriously doubt that I would be, but I'm never sure what to say. If I say no, I feel like I'm kind of lying or not really answering the right question. If I say yes, I don't really know what happens...
You're right, while using contraceptives like the pill or condoms do provide really excellent protection from pregnancy (especially when taken/used absolutely correctly all the time), nothing is 100% except completely abstaining.
Probably the best thing to do is to give a more detailed answer. Simple "yes" or "no" answers often don't give enough information (for example, sometimes people have risks that they do not recognize because they don't know they're not using their contraceptives correctly, etc.). You could say, "I am sexually active, but I take my birth control pills consistently and on time and I always use condoms for all genital contact." Or, "I am sexually active and I take my birth control pills consistently, but my partner and I do not regularly use condoms." Or, "I am sexually active, but I don't always take my birth control at the same time each day." Or whatever else might be the case. Obviously you don't have to give out all the details of your sex life, but by being specific about what contraceptive method(s) you are using and how you are using them, you will be both telling the truth and be giving your health care provider the information they actually need. By giving your provider all the information, they will be able to better assess what tests or treatment to give (depending upon exactly what you've been seen for). If they believe you have had a risk, they might want to do a quick pregnancy test before deciding on a diagnosis or treatment.