I tried supplements like milk thislte and fenugreek tablets. Also lactation cookies which has brewers yeast and oats in them. You can get brewers yeast at health food stores and recipes on line. Or there are some really tasty ones from Franjo’s kitchen. I don’t know if they really work, but you can always try.

First of all the amount of milk that you can pump is not an accurate measure of your milk supply. A baby with a healthy suck milks your breast much more efficiently than any pump. Also, pumping is an acquired skill (different than nursing), and can be very dependent on the type of pump. Some women who have abundant milk supplies are unable to get any milk when they pump. In addition, it is very common and normal for pumping output to decrease over time.
I read your bub is 11 months old. Has your bub maybe started eating more solids lately ? Milk production is a demand & supply process. To speed milk production and increase overall milk supply, the key is to remove more milk from the breast and to do this frequently, so that less milk accumulates in the breast between feedings. So the best way to increase your production is to nurse frequently, as often and as long your baby wants and offer both sides.
Did you try switch nursing ? Switch nursing is when you switch sides 3 or more times during each feeding, every time that baby falls asleep, switches to “comfort” sucking, or loses interest. Use each side at least twice per feeding. Use breast compression to keep baby feeding longer.
Also avoid pacifiers and bottles when possible and you can try herbs like fenugreek to increase your supply.

I tried fenugreek tea , not sure if it worked, I also expressed more often

I would definitely talk to your GP. They are so good!

At 11 months bub probably isn’t drinking as much so maybe it’s your body just sorting itself out. Oats are meant to be very good to help increase milk supply though. I have an 11 month old and lately he has only been interested in milk for the first 2 feeds of the day. I try for 5 times but for the last 3 nights he hasn’t really fed before bed at night. He’s just getting older and eating more i guess.

maybe it is just your body adjusting to the needs of your child. Bub is probably eating a lot of food at 11months and won’t take as much milk so don’t worry

One theory is that continually expressing milk dries your milk up quicker. I have heard a few Mums comment about it.

I’ve heard Lactation Cookies are great, you can by them or make them yourself by just googling the recipe. I’ve heard beer can bring more. My first baby I didn’t have much so I had to bottle feed at 4 months but with my second & third I had plenty.