Extreme fatigue after eating

For the past two weeks or so, I get extremely tired after I eat. Not "I have the itis and wanna sleep" tired, but I can't bear to stand up or walk around tired. I assume (and have read online) that it's just because my body is so busy doing everything else that it just gets overwhelmed. It's unfortunate because I work retail and can't just relax for an hour after I eat.