When to buy pregnancy clothes?

A🕊 • 34. Married to DH for 9 years. #1 born 2016. #2 born 2018. Fertility issues - Tried 3 IUIs. Army wife. LDS.
I'm extremely early in my pregnancy but I'm worried that because of the way I'm built and the way my clothes fit now, that I won't be able to wear my normal clothes for too long. Especially if I gain weight anywhere besides my belly, like my upper arms or thighs/butt. When did you transition into maternity clothes? I'm already dreaming of maternity pants.