Signs of Cheating?

My boyfriend and I have been dating for almost 5 months now. We've never fought or have any disagreement. We connect very well and he is the type of guy who I've been looking for.

We communicate daily. At first, I didn't have strong feelings for him but when he told me how strongly he felt about me, I developed strong feelings for him.

Recently, he didn't contact me for 4 days and didn't respond to my sms. When I called him, he got back to me with a text message.

What's really happening? This feels awkward to me and I sense that he has someone else. Do you think that this could be true? What are the signs of cheaing? I really need help.