Hi Dan, you just need to try changing things up. When doctors tell you what to inject its really just their best guess, they don't actually know off hand what exactly you need.
For examples when i was diagnosed i was told to inject 6 units of novo rapid before every meal minimum plus more if I was above 8mmol/L i did that for about a week and was constantly low.. jump through all the changes to now, and i RARELY ever need more then 3 units for a meal. There was meals i was inject 7-9units! Those same meals i now only inject like 3..
Point is, i felt the exact same way, i felt like they screwed up the diagnoses, but really its just that you need to play with your doses and get them to a point where they are proper.