Any of the above, but not immediately before your exercise routine. But what you really need is a general overhaul on your whole diet regimen if you're tiring out before your finished.
There's also the possibility that you just need to show a bit more patience while your body adjusts itself to its new routine. Wait til the seratonin kicks in, then your body will be begging for more.
And finally, you might want to try a B12/B6/Folic Acid complex. The one I take gives the most amazing results in overcoming any fatigue due to extra physical strain, or even stress. Typically, I take one in the morning, but if I'm expecting a difficult day for some reason, I just pop another under my tongue around noon, and my energy will hold up until the pillow beckons that night.