Im 28 weeks pregnant with my 1st, i felt kicks at 19 weeks and my boyfriend was able to feel her at 21 weeks. I didn't exactly have a flat stomach before i got pregnant either. Try drinking something like orange juice and lay flat on the floor, if the baby is laying right u might be able to feel it. That's what i did sometimes and it worked
I wouldn't worry too much about it. Some babies you can't feel from the outside until like... 25+ weeks. Their movement just isn't strong enough yet to feel from the outside. I didn't feel any outside movement until I was about... I want to say 30 weeks with my son... Soon enough you'll feel it outside.