*hugs* I have had low supply from day 1. Thanks to getting a cold in the hospital, which delayed my milk coming in, I have just been messed up from day 1. I worked really hard to be able to breastfeed in the first 6 months, and still always supplemented with formula. Honestly, I cried the first time I gave DS a bottle of formula by myself. I had to hold back tears when I did it at the lactation consultants office. It is HARD.
When DS started solids my supply tanked again. And it's still going down. He has a hard time nursing because he's super distractible and it takes forever to get a letdown. So that doesn't help. He's getting more supplements now than he did before.
I don't think that there is a magic method to giving BM or formula and in what order. I only pump once a day - at night when DS refuses to nurse at all. During the day, I nurse in the AM and after naps. Then he has a couple more ounces (or however much he wants) after nursing. At one of those times he'll get the BM supplement before the formula supplement. Sometimes I just freeze the milk so that when DH is watching the baby he can give him BM instead of formula. But really, there is no rhyme or reason!
Some other supplements I found helpful: More Milk Plus (by Motherlove), Chlorophyll with Papain, Brewer's Yeast, eating lots of oatmeal, drinking lots of water. No sage!
Another thing that made me feel a little better about giving formula was researching and finding one I felt comfortable with. We ended up with Earth's Best Organic formula. I figured if I have to give it to him, at least he can have organic.
Really, it will only take time for you to kind of come to terms with it. I still have my moments where I wish that I could have had the whole EBF thing and have it easy. On top of low supply I struggled with plugged ducts (which probably didn't help the supply!) Just know that you ARE a good mom - just by trying to find some help for the situation and being upset about it shows that. My LC told me that the ratio of BM to formula is not equal to the benefits. Like 50/50 of BM and formula doesn't mean they're only getting 50% of the benefit of BM. It's actually much higher than that. And ANY BM is great
Oh, another thought, is it possible you are getting your period? I know that can sometimes greatly diminish a supply when you're about to have it. Kellymom.com has info on it and how to battle it by taking Calcium and I think magnesium.
*hugs* again