Try taking the second dose later in the afternoon, your taking the second dose too soon, that would account for crashing in the early evening, I take the first
30 at 9am and the second
30 at 4pm. You just have to use trial and error with the second dose, just don't get too close to bedtime or it may keep you awake, or just take the morning dose, then see how long it lasts, then when you start to feel a little down, then you can estimate the time for the second.