HI there- congratulations onf the birth of Lachlan!
Isabelle got hiccups once a day when I was pg and she still gets them now also at least once a day although its seems she got them more when she was a bit younger! Im sure its pretty common but Im not sure what its from. I find that I dont worry about it unless she is about to go have a nap and i know it will keep her up so I put her back on the bb for about a minute to get rid of them! HtH!