It's hard to know without seeing what you eat, but are you sure it's enough? Have you tried tracking a few days to see if you're hitting high enough calories? I'm really stuffing myself at night.. and from others I've talked to, it's very easy for them to under-eat.
My sport (track cycling) is very power intensive and has both strength and endurance components.
I have two eating periods on active days and one on my rest days. That seems to do me ok, but endurance has still been an issue.