Could I be Pregnant? Please help!?

I had unprotected on Oct 17th period came on 20th but only for 2 days and was very light. It's usually is on for 5 and is heavy for the 1st 3-4 days and light on the 5th. In november it came 5 days early (usually have 28 day cycles like clockwork). It was also very light and lasted 2 days. My are very tender tender and I feel so tired all of the time. 25 years old. Please tell me my body is just going through a change. Also had some unusual pains in my belly on.