Is it normal to interview for faculty positions in December-February and not hear back yet by the end of March? I had several interviews in December-February in R1 universities for tenure-track assistant professor positions in a life sciences field. 

I was told that they would get back to me in March, so I emailed them and some have not replied back and some said to wait some more. 

So, I was wondering if this is normal to wait for that long or "the ship has sailed" and I'm not getting any offers :(
Commiserations -- the job search is tough.

If they haven't gotten back to you by the time they said they would, it most likely means you are not their first preference candidate. They probably have already made an offer and are waiting to have that accepted or rejected. You could still get an offer as their second/third/fourth/etc. preference.