im 16 weeks 5 days and i started having cramps a few days ago. i was told its the uterus and the surrounding muscles stretching since from now the baby is rapidly growing :)
Oh and im 15 and 5 by the way
I get them sometimes too. My doctor said that because i am so thin i will probably feel them through out my whole pregnancy
I'm 16 weeks as well and started exoerencing the same thing about 2 days ago, i found that drinking a lot of water helps reduce them. but its probably to be expected to have some "growing pains" as the baby is growing much more quickly at this point.