How do I handle my girlfriend always wanting more?

My girlfriend and I have been going out for about a year now. I was her first and the relationship has been great.

However, things have been changing a little of late. It’s now got the point that every time we meet she wants sex, no matter who may be in the house with us etc. And she will push and push for it no matter what my response may be. And if she doesn’t get it then I will find myself ignored for the rest of the evening and made to feel massively guilty. It has now got the the point that I have done the deed regardless of whether I really want to so as to save any bother however I feel that it cheapens the act.

She sees it as a cold rejection. That I dont love her enough or find her attractive enough. Where in reality I don’t feel well or have had a particularly horrible day at work.

It’s starting to bother me quite a lot as the relationship other than this is brilliant.

Any help and advice would be massively appreciated.