Are you the sole wage earner? I hear a lot of pressure from what you wrote.
I have experienced a thing with my former boyfriend and your post reminded me of that time. He was in trouble and felt ashamed of it, so he tried to do everything alone and keep it from me. He didn't want me to see his problems (emotional, financial and problems finishing his bachelor degree). He thought he would fail in university, he was poor and he had some family issues as well. He couldn't sleep, was very stressed out and I worried constantly because I felt that something was wrong but he wouldn't tell me. I would have loved to be there for him and it made me sad that he didn't trust me.
How do you think your girlfriend would react if you were honest about the uncomfortable things? Are you afraid that she might leave you etc?