When is it time to buy maternity clothes?

Alexandra • Mother of one amazing 19 month old girl and trying for a second.
So when are you planning on buying or who has already bought some maternity clothes? I work in a professional setting and have found my pants becoming uncomfortable. I am wondering if it is almost time to think about some maternity pants. Any recommendations on wear to find professional maternity pants? I am 13 weeks with my first. Thanks in advance!