Spotting?

I'm 21 weeks with 3 days and last night at around 2 am I went to the restroom n when I wiped myself there was a bit of blood..not a whole lot just a little and I made sure it wasn't from.anywhere else .... I'm concerned cause this would b the second time this happens..when I was 18 weeks I also spotted ... I called my OB and she said she'd get back to me so I'm waiting on her call back so meanwhile I'd like to know if this is normal? It wasn't a whole lot of blood just a little and it wasn't dark it was light red..please comment