When did your clothes get tight fitting in pregnancy?

I am estimated to be 10 weeks pregnant as of today (I've not had a prenatal visit yet, but I will soon, so this is only based on my last period) and all the websites I have looked at said that my pants should be feeling tight now and my bra should be tight/small. However, none of this has happened. My pants from pre-pregnancy still fit exactly the same, even the ones that were too big are still too big, and my bra fits me exactly the same as before. Should I be worried?

This is my first child. I am 22 years old and have a small build. Much of my family believes I will only get big in my belly and I probably won't even begin to show until I'm about 5 or 6 months pregnant.