re: Is this normal in a relationship?

I've had two children and both times in the first year there was a period where my husband and I didn't like each other very much. It really wasn't that our relationship was doomed, just that we were going through a very difficult time exacerbated by being tired and emotionally exhausted taking care of a creature that can't do anything except take. We weren't taking care of ourselves or each other. It was temporary and we pushed through and we found our happy together again both times.

Does your girlfriend do most of the childcare? Because if so, she might be burned out. My husband has never been an infant/baby person so I naturally took on most the of the care the first year. It wears on you and it is very easy to slip into resentment because while the father may have had a big change in his life, reality is that mom's life/body/hormones/mental health has been through the wringer. If she hasn't been able to take care of herself (which is 99% of first year moms I personally know) and you haven't been taking care of her and been gradually taking on more childcare after the newborn phase, she is probably going to be cranky and not pleasant to be around. My husband took on more when our kids started walking and eating regular food (so a year old). Strangely, this is when we stopped hating each other both times.

TL;DR- Don't make permanent decisions on what might be temporary feelings/situation.