Something serious or am I being paranoid?

Ever since late last night, I've been feeling pains in lower stomach that I can't distinguish between cramps or gas. I know the whole ligament stretching thing can cause cramps and I've felt that before. This is worse, twice it's brought me to tears. Then out of nowhere, my lower back in my left side started to hurt. This is my first pregnancy, so I'm wondering if I'm just being paranoid. But if it's something serious, I'd like to know. I'm 16 weeks and 3 days.