How many weeks for maternity clothes?

Cara • Expecting our first baby Jan 1st 2016! Married my best friend after 8 years together 10/10/14.
I'm just 5 weeks along. I'm about 5'2 and 128lbs. I keep seeing that maternity clothes aren't needed until a few months into pregnancy. I don't need them now I'm not big enough but even at 5 weeks my pants are tight around my belly area. I know it's just bloating at this point but they're still slowly getting tight.