milk supply down?

i had my baby June 1st (she is a little over three weeks). i had been breastfeeding only. last friday when she was 2.5 weeks old i had a dr appt and she was back up above her birth weight so everything was looking good. then this week she started wanting to nurse constantly, was really fussy, and i noticed she was peeing a lot less. we took her in to the doctor and she had lost 8 ounces in the 5 days since the last appt (!) i saw the lactation consultant who said her latch looks good, my positioning seemed fine, so it must be a supply issue. now i’m nursing, pumping after each nursing session, and supplementing with formula for her.

has anyone experienced a sudden decrease in supply like this? the doctor thought it was strange since everything was going alright as of last week ;asked me if i was sick or if anything changed which it didn’t from what i can think of)

will i be able to get my supply back up?! we are having to give her so much formula (1-2 oz every time i nurse) i just feel like i’ll never be able to produce that much more!