Doc says I'm not getting enough calories. Help?

I've been weight lifting for about a month and I've progressively gotten more and more tired and it's been getting harder. My doc says I'm not getting enough calories and I had been doing 1500 and struggled to get that in. He says I should be doing 2000 and look to add that in with my protein drinks.

anyone else have this issue?

How are your lab numbers? It could be low iron or B12...