I had the exact same experience, however we'd been together longer.
It was as if a switch was flipped one Monday. I went from having a phone call or at least a text every lunch time to no contact all day, or the bare minimum at least. I pushed it off as I knew he was busy, but after it was the same the week after and I honestly felt so low and down I asked him. He swore he didn't realise he was doing it etc and was just busy, but it killed me every time I would go on my phone and see that he'd been active on WhatsApp and had ignored my message - but clearly had replied to someone else's. After a month he did 'perk up' a bit and we were fine - probably better than fine. Then, he turned up on my doorstep crying and broke up with me one evening quite randomly. I do chuckle now because I ended up comforting him... through my own breakup
?
Anyways, the point I am trying to make is do not ignore your gut. My gut was screaming at me that something was off as I would sit at my work desk and be silently crying because all the potential scenarios would be running through my head (i.e does he want someone else? am i not enough? have i done something wrong?) and it honestly ruined me for almost 5 weeks of my life, which isn't long but felt like a lifetime. I wish I'd have been straighter with him after I was making myself unwell over it and maybe then he'd have been honest with me about our relationship or would have bucked up his ideas? I don't know, but please don't take his behaviour as normal. Yes the honeymoon phase finishes, but he should still want to spend time with you or at least touch you when you are together. Once that's gone, you really need to speak to him for your own sanity xx