Loss of sex drive is very common in the first year of sobriety. It can take a while for your body to return to homeostasis.
As a male who had a high sex drive, even while intoxicated, I had basically no desire for the 6-8 months of sobriety. I was single my first year of sobriety (at the suggestion of my sponsor), but there was no urge for even self-pleasure.
But it did return to normal. If you don't start feeling more like yourself after about 6 months, you can always talk to your doctor.
I wouldn't worry about it. Concentrate on your recovery. If your girlfriend brings it up, it's ok to be honest about what you're feeling, or rather, not feeling. Make it clear it has nothing to do with her. Things will get better if you stay sober. And sex is far more enjoyable in sobriety. It's worth the wait for your body to heal up.