Most Helpful Guy
Everyone has ups and downs. My girlfriend has seen me at my best and at my worst. Some days we can sit and talk for hours and others we sit and watch Downton Abby for hours with very little words spoken.
If he seems to generally enjoy spending his time with you I'm sure you've got nothing to worry about.
Most Helpful Girl
I'd say it's pretty normal.
Everyone will experience varying levels of how openly affectionate they are with their s/o. He could be not feeling too well, or have his mind focused more on work/school related things. If he's stressed, that will also affect how much he acts on his interest in you and such.
Don't take it personally. There'll probably be many ups and downs like that from both of you throughout the relationship.