3.6mm endometrial thickness w/ clomid

So I took clomid this month and have 4 good sized follicles around 20mm some above and some a little below but during the ultrasound CD 12 they found that my endometrial thickness is 3.6mm. My doc said we might do some estrogen with the clomid next month. Has anyone experience this with a good outcome? Isn’t the purpose of clomid is to trick your body into make more estrogen already??

I’ve been ttc for about 6ish years with no success so maybe this has been my issue all along?