Tummy tensing up on its own? please help!?

lately before bed i will start falling asleep and my tummy would tense up on its own i can't control it. Its kind of like when you need to throw up and you tense up your stomach to throw up but i don't need to throw up. i just had a baby on march 30th the last time this happened to me was when i was pregnant. i keep searching online trying to figure out what is wrong some people say anxiety. after that night i been scared to go to bed and laying in bed hoping my stomach don't tense up and since im thinking about it i think that's why it happens. please help me with anything you might know im scared and confused i just want to go to bed like a normal person. it is really bothering me. should i go to the doctor? i want to know why this is happening to me ... thank you :(