Everyone is different. If your clothes are too tight then by all means get maternity clothes! Don't wear pants that are too tight! Wear whatever FEELS comfortable for YOU! You'll need to wear different clothes as you grow; one pair of maternity pants won't fit you through your entire pregnancy. For me (now at 35 weeks) I've only got one pair of pants that are really roomy and comfortable! (gotta do lots of laundry but I only sit around the house every day so whatever!

) My "big elastic banded jeans" are too tight and have been for quite some time and my pair of expensive nice maternity pants are a bit tight as well and I only suffer with then when I want to look nice. The bottom line is you have to just wear whats right for you at the time, there are no set rules as to when to start wearing maternity clothes!