if it feels like it's moving and it hurts it's probably gas but the first time I felt mine was also when I was 18 week and 5 days I felt a little bubble air on my stomach :)
It depends on the baby as well my first was so lazy t hi s one is very active . around 28 weeks is when you will start tracking the movements there is a good app for it.
I was 19 when i found out i was pregant and this is my first baby as well i didnt feel her move until like the 22 or 23 weeks pregant....so u wont feel him/her kicking yet
Normally 1st pregnancy most women don't feel the baby till about 25+ weeks I felt mine at 22 weeks