Even though you say it doesn't feel like normal gas, most likely, that's exactly what it is. I have had this EXACT feeling, and thought I was totally going crazy because it feels exactly like it did when my kids kicked me during pregnancy. It could also be your intestines having a spasm. If it hurts at all or bothers you that much, you should see your primary care physician.
Twitching is from a muscle, perhaps a nerve causing the muscle to twitch? If it is painful or particularly bothering you, please see a physician.