increase supply/supplementing

Katie • High school sweethearts! We have been together since 10.19.07 (Married since 10.19.13).We have 1 Angel baby❤ March2016. 1 Girl 02.07.17, 1 Boy 05.18.18, & Girl 04.07.22

my daughter is 8.5 months old. I am a working momma so I pump at work to get bottles for when I'm gone. this has worked out so well for us so far. I am currently about 8 weeks pregnant. my supply is plummeting.. don't know if it is the hormones from the pregnancy, stress from work, worry about not having an ultrasound yet to make sure this baby is growing good..so many factors I'm sure. I am making sure to drink lots of water & I take a yeast vitamin along with my prenantals. can't seem to get my supply back. Anyone have tips/ tricks for increasing my supply or opinions on what formula to supplement with? my freezer stash is now gone and I am only getting 1.5-2 bottles while pumping when she normally needs 3-4 while I'm at work