Try to stay positive and take deep breaths, your body is doing a beautiful job of growing your little one. Tightness is often just stretching or gas, but if you feel any sharp pain, do consult your doctor. Keep drinking water and stay calm.
When my tummy felt tight, my mother would make me lie down on my left side and give me some warm water. Usually, it's just the body preparing itself, but if the tightness comes with pain, please call your doctor immediately.
I had thyroid issues and had to be very careful with any unusual symptoms. Tightness can be due to dehydration or Braxton Hicks, but it's always best to mention it during your regular doctor check-up to rule out any pre-term issues.
This used to happen to me a lot in my third trimester, feels like the tummy turns into a hard ball for a few seconds. My gynac told me these are Braxton Hicks contractions which are normal, but if they get painful or don't stop, please contact your doctor immediately.
Because of my delicate IVF journey, every little tightness used to scare me. Often it is just your uterus stretching or minor gas, but please check with your doctor if it happens frequently. Drink some warm water and rest for a bit to see if it eases.