I'm on birth control, and lately have been very dizzy/light-headed often. could i be pregnant if this is my only symptom?

Unlikely: If you take the pill regularly, you are unlikely to be pregnant. If you missed your period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine.