I posted a similar message a few months back but only got a small number of responses, most of which were in the vein of "welcome to parenthood".
I don't think it necessarily means there are relationship problems. How old is your DC if you don't mind me asking?
I had a lot of time and energy for sex before DD, now it's less important to me. I think being a parent fulfils a lot of the need for sex i previously had (if that doesn't sound odd, you know what I mean?).
Being a parent also generally means less sleep, more things to consider on a minute-by-minute basis, literally less energy, emotional and physical for sex.
I also have hang-ups about my body which make me less adventurous than before (a lot less). I don't have any stretch-marks, but my neather regions are somewhat altered and I am very conscious of it.
Only you know what you are thinking and feeling about sex. But I would say if your DC is under one, give yourself time.