Too tired

Okay ladies, I just really don't know what to do. I just started a new 8-5 job working every week day, I am in three summer school classes, and I work weekends as a server. Because of this I don't see my friends really ever and I hang out with my boyfriend every chance we get. The main issue is that when we hang out and he is starting to initiate play time or sex time, I am so freaking tired. I honestly have to force myself to fool around (even though I would love to if I wasn't so tired). But I am getting so tired and I know he wouldn't care if I just didn't do anything but I feel bad. The last couple of times I have just pushed him away, which I have never done before. Help !