Clingy Baby sleeping for more than 12 hours 😱

My very clingy 3.5 month old who needs to be held to sleep and only sleeps for like 3 hours at a stretch has been asleep for almost 13 hours now. He didn’t even wake up for his middle of the night milk. I’ve been checking on him and he’s okay. I just find it strange. He had his first round of vaccinations yesterday. Could this be why he’s so sleepy ?