By the way, there is an adult ADD site that has some very good info (if you can navigate to find it as the writer has ADD and it shows). Anyway, you might want to check it out. its http://jeffsaddmind.com/for-first-time-visitors
If I read your two posts correctly, you have only been on V for two weeks. It does work for you but ends to early. You take it very early in the day.
First the ratings for it say 8 to 12 hours. You might want to try and take it a bit later in the day. Also you say how tired you are for the kids. That is very understandable. You have been working all day. Heck, I would be very tired too. Any stimulant med when used by someone with ADHD really won't "stimulate" you like it would for a person with out ADHD. There is a reason the military uses it for there long range pilots. You can't expect it to work like that for you. Physically, are you ok? Not anemic, sleep well at night, good diet, etc?
And yes, it is a guessing game because everybody is different. Here is a post that may help you - http://www.corepsych.com/2009/06/vyvanse-dosage-for-adhd-finding-the-safe-top-of-the-window/ and check out the blogs he mentions.
There is also a good chance that when you tried the adderall, you took too much. With all the these meds, you need to start slowly and let your body get used to them. Same thing might be true for the V. At any rate, do talk with your doc after reading up some more on V. This also might help - http://www.addadhdblog.com/vyvanse-dosage-how-to-get-the-right-dose/#c987e
Hope this helps. Best wishes. Let me know if you need any more info.