That's the likely culprit for my issues, I have not been able to achieve a normal supply for my girls either. (Especially DD1 didn't even gain 200g by 3 weeks and was getting dehydrated etc) I did notice a little development with my second pregnancy and my supply was improved but still only about 50-75% of a supply, herbs, accupuncutre and motillium did not work for me. Goats rue is the main herb celebrated for insufficient development if that is the case, but there are others. There is a fantastic book called Making More Milk written by Lactation Consultants who have experienced and made a study of women with true insufficient supplies and has fantastic advice and suggestions for various methods you can try. I mixed fed my girls (Formula Comped) until DD1 refused breast at 7 months, and dd2 Refused bottle at 8 months and was just a booby girl till recently when she decided she'd take one again which i never thought I'd be pleased about but I really am.

If the LC you see doesn't seem helpful, it can be a good idea to find one who will take what you are saying seriously and see if they can come up with a proper approach for you or at least see if they agree with what you think may be the issue (in my experience every LC I met IRL glossed over the issue with the supply=demand just feed more speech that made crap wad of a difference to my stupid boobs and non-thriving babies, so you may want to go private if you go down that road). I'm sorry my story wasn't a 100% success for you, but I highly recommend the book, it has some great success stories in it, and in the end, helped me to come to terms with what I CAN do and keep that up. All the best, I'm hoping things are easier for you this time around