Am I being too sweet? And how to balance dating your best friend... (long)

Ok, so I recently started dating a girl, I'm in college now and she's my best friend from High School (One grade below me) and we live about an hour and a half away, so I generally get to see her about every other week. So since she was one of my best friends we're really comfortable with about anything and whatever and whatnot.

Well, she's been in some moods for the past few days due to her period, and she has a migraine, as well as lots of school and parent stress going on. And I understand this and try to do my best, but it just seems like every time I talk to her she's upset with me or something... and it's just majorly hard to deal with and to keep on smiling and being happy I'm with her whenever it seems like she's been in a constant b*tch mood lately

Well anyways, I asked her out, and I must admit I have been doing lots of things (I bought her a flower on 2 of the three times I saw her and the third time a little bunny I saw) for her. However, I've always just seen that as me and it's what I do, I enjoy doing little sweet things for my girlfriend and complimenting throughout the day and things of the sort.

Well, long story short, she keeps telling me to stop being so sweet (and she's serious when she says it) So I keep trying not to be so cutesy or whatever, and I think I'm making progress haha, she still says it on occasion but yea. Should I try and not be so cute? Or is it just the mood, or whatever and what not... This leads to my second problem

She says I'm too happy... I'm a very optimistic and always in a good mood and look on the brighter side of things (generally) like she's feeling sick and I told her that I'm sure she would be feeling better, she respondedwith "Stop being so positive it's making me more negative" which kinda shot me and made me feel bad, cause, I've always been complimented and had smiles on my upbeat mood (hell, I've had some people ask me if I was gay due to the fact I was "too happy"). I mean, should I really try and change my optimistic view? Or should I just try not to be so hopeful and joyful when I talk to her when she's down or what...

Example: I asked her to text me when things went ok (she was in a bad mood and couldn't call me because of parents) and so she called me and was hey, I'm f*ing tired so I asked her if she wanted me to let her go to sleep, and she responded with no I called you so why the hell would I want to go to sleep?

And yea, then another thing is, because she was my best friend, she wants to continue being my best friend (I want that too) as well as my girlfriend, and yea, just need any advice on how to continue being that best friend with her and only going into "relationship" mode when place requires haha...

Yea, it's just been getting to me, and I really want this relationship to work (because when she hasn't been in her moods she's been naught but amazing) and not to mention if anything happened I wouldn't just lose a valuable relationship I care about, but a best friend as well...

Anyways, sorry this has been so long and if anyone can give any advice it would be appreciated like woah =[

Sincerely,

Andrew