17 & keep on getting negative test?

So I've been trying to get pregnant since February .. & always still now close to my periods 2 days before my periods I'd spot pink redish brown.. Still now.. Myappetite chnaged so much , I don't eat as much no more , but I'm still getting bigger my belly is getting bigger & sitting up more .. I haven't been to the doctors yet .. I keep on getting negatives pregnancy test .. But is it possible to get negatives & still be pregnant?also stretch marks have been forming like crazy & itching & I've been very nausea .. I like pickles but I hate the smell of them.. I've been smelling more then usual .. Also peeing more ..