No worries...with both my pregnancies I didn't really pop until the end. I am 40+4 and still wearing pre-pregnancy clothes, and he's growing just fine.
I'm 22+4 also size 18 and no baby bump :(
I was seven months with my first baby and still wearing my everyday clothes with ease so I wouldn't worry to much cause she was 9 lbs when she was born and as healthy as can be.
Im 19 weeks and five days and I have no baby bump either. I went for my anatomy scan friday and baby is measuring perfectly and she weighs about 10 ounces! With my son I blew up at about 22 to 23 weeks it seemef as if I went to sleep and woke up huge lol
I was about size 8-9 with DS and didn't get bigger until like 25-26 weeks, some women it just takes longer to show! Don't stress about it, I'm sure you're just fine!!