Cramps

Last night I was having period like cramps and my lower back was hurting, also felt a sharp pain on the lower right side by my hip every once in awhile, it scared me so I checked for a heartbeat and found it right away. Then today I started getting a sharp pain on my lower left side it would come and go but last a few seconds. I also tried to find the heartbeat usually it’s lower by my hip but this time I found it just under my belly button so I guess the baby moved. My doctor said this is either cramps from being constipated or just the baby growing but it’s freaking me out.