TMI question about sex

Okay my husband and I have been together for 5 years. When we have sex normally it is like 20 to 45 minutes. I've noticed the last couple weeks it's been taking like 3 minutes tops. Why would this have drastically change? He said he doesn't know. I don't know if it's because I'm pregnant but I'm only about 13 weeks. Or could it Be age? He's only 33. Is not really a big deal I just noticed the difference and I was wondering why