tight belly off and on 18 weeks pregnant

so I'm 19 weeks on Monday and today I've woke up to my tummy feeling tight but comes and goes. I've heard people say braxon hicks does that mean I'm going into labour lol? I'm so confused idk if it's due to my uterus stretching as well! also have not been able to pass bowels as I've been so constipated carrying him so I don't know if that's the reason being as well. please let me know ur thoughts on this 🙂