Shopping for Maternity Clothes

My mom and I are trying to plan a day to go to the outlets to do some maternity shopping. I'm a thrift shopper but she wants to take me as a birthday present (it was in March lol) Anyway, I'm 16 weeks and have bought two pairs or pants and a pair of shorts. My winter stuff is more baggy and work related. I'm a teacher. My summer stuff is usually tighter and I'm noticing none of my summer stuff from last year is fitting me now already. I'm really not sure if I should be buying maternity clothes yet. Will I grow out of smaller sizes? The two pairs of pants I bought are a little too big in the butt and thighs area and I only bought them because they were $3 lol Do I buy what fits now as long as the belly comes all the way up?