at 18 weeks baby isnt very high but also has a lot of room to turn somersaults and roll about a lot in there.
Id say that what youre feeling is more than likely just lots of playing by littleboo but check with midwife anyway.
I recall little CRX having hiccups a lot when i was carrying him and that was always a strange feeling.
when further on in pregnancy you will feel firmer pushes and kicks and at the end when baby is head down the kicks will be at your ribs and the punches will be around your cervix, not a comfy feeling at all.