Maternity clothes?!

Jess • Expecting baby #5 🌈 after losing Baby #4 at 11 weeks RIP 12-23-14
I am currently 20 weeks with my 5th child (a rainbow baby). My belly feels much bigger than the last 3 full term babies did at this stage. At what week did your belly "pop" and you had to switch from regular clothes to maternity clothes? So many people have said I look "too big" to only be 20 weeks. :( All my babies have been full term an small- 7.3lbs, 6.14lbs, 5.15lbs. Help!