V should last you 10+ hours. If it does not that typically is a sign that you are under dosed and need a stronger dose. Crashing 3 to 4 hours into the day would also indicate that, although you should also have the same problem I would think around the 6/7 hour mark.
Anyway, you need to talk with your doc and get that opinion. My own opinion would be to try a stronger version of V first - mainly because it is a more gentle release and you don't have to remember to take the other pills.
By the way, if you are not having a high protein breakfast, make sure you do that first and see if that makes a difference.
Hope this helps.!!