Im also in my first pregnancy (14 weeks) and I have also experienced these cramp-like aches. As long as they are dull, and bearable, they are normal. Your uterus is probably just stretching along with all other muscles in your hips, and back to allow room for the baby. If the cramps become unbearable, or if you notice you are bleeding, then you should seek medical help. Also, if you need the comfort of hearing from a doctor, then I would go just to feel better about it. At 16 weeks, USUALLY you are out of harms way!

Take care!