I started saying i love you when my i know i actually did love the girl, it was about 3 weeks into the relationship, and guess what? she said i love you back. Now, when i talk to her on the phone everyday, and we expressed our feelings like every 5 minutes, and its the best thing ever because i know she actually meant it. Not just saying it just to make me happy but because thats what she felt.
So my advice is just go ahead, express your feelings to her, theres basically nothing to lose. If she doesn't respond to your liking, maybe you should re-evaluate your relationship or give it some more time. Oh and make sure you tell her what you love about her, girls love compliments.
It's never too soon to express your feelings but make sure you are absolutely sure about it. Once you let it slip, it'll be more easier each time.
Also, i did know a guy who said "i love you" to the girl that he was dating just for sex, and when she got too attached, he freaked out. People like him are bastards and i hope you are not one of them.
