Could I be pregnant or am I just worrying too much??

So I'm on the pill and it makes it where I only get my period every three months. My husband and I never use any other protection except bc and the "pull out method" so it's still possible. Here recently I've been feeling nauseous in the morning and at night, also any time I eat a big meal but never throw up. Also I've had headaches every day almost, I'm very tired all the time & dizzy among a few other symptoms. The past few days I've had that like brown stuff that happens when you're coming off your period but no period and got two negative tests but took them about 2 weeks ago. Could I be pregnant and it won't show up on a home test or am I just paranoid?