It’s happened to me a few times as well. What helps is to lie down if you're sitting or walking, and make sure to drink plenty of water. It tends to happen more when you're not properly hydrated. I’d still recommend consulting your doctor just to be safe, but it could be normal. As long as you're not experiencing back pain or actual contractions, they’ll probably tell you it’s fine.
37 weeks today and currently experiencing this
I have been experiencing stomach tightening from past 2 hours. I dont know what to do :/