It's not uncommon. I would say out of 15 preps I experienced it the first two or three times. In my fisrt preos, I just cut fat far to drastically. Nowadays I never go below something like 80g of fat, even in the last few weeks (except the deloading/loading week).
This helped a lot.
Another thing I believe helped me - though I can't prove it - is the addition of vitamin D and E.
I keep red meat in my contest diets until the end, which seems to keep my energy higher.
I eraly times, I just went too low on calories and fats. I prefer having a higher energy turnover in my preps now, i.e. I do much more workouts a week (7-11 compared to 4-5). This way I can keep my calories higher.
One more thing: I feel the nervous system is key in contest prepeartions. Try not to burn out. Try to avoid grinding in your workouts. Try neural recovery workouts.
This might help to keep your libido high as well.