Hi mama! Totally normal yan, marami sa amin na first-time moms ang hindi consistent ang movements sa 18 weeks, some days parang walang movements talaga, then biglang maraming activity, so huwag mag-alala muna. The back pain is super common din sa pregnancy, but since you're also feeling kirot and want to make sure everything's okay, best na i-check mo with your OB para ma-confirm kung lahat ay normal lang at walang concerns, kaya peace of mind ka na agad!