Mood swings - common during a new relationship?

My boyfriend and I are together since Oct. '17, and we are a couple since 26th Dec. '17. I am very happy in my relationship, but we are still quite young. I often get feelings where I doubt he loves me as much as I love him (early days to say that, I know. But i suppose we are in the 'honeymoon' phase). I also get days where i am so grateful to have him and I cant imagine myself with anyone else. Overall, I am the happiest Ive ever been but i worry i am being too optimistic.