Normal lang yan, lalo na pag gutom ka talaga, minsan ang uterus ay nag-contract pa when you're hungry, kaya parang hard or tight ang puson mo, pero once kumain ka na bubilis ang movements ng baby. A few of us moms noticed the same thing, especially pag umaga and we haven't eaten yet, parang nag-tense ang belly. But since you're feeling baby move after eating, that's a good sign, it means baby is responsive. If it ever feels painful or the hardness doesn't go away even after eating, best to check with your OB just to be safe, pero from what you're describing it sounds okay na.