I have been with my boyfriend for over a year now and always have unprotected sex because I thought I couldn't get pregnant because I have only had about 3 periods this year. Anyway I took a test at the hospital and it came back negative but I'm nauseous a lot mostly at night my nipples are sore my stomach is hard everything makes me cry I have been getting head aches and body aches flue like symptoms when I have intercourse it feels like he is hitting something in my stomach my belly button is really hard... help please :)

Hitting something hard during sex is not a pregnancy sign. What were you at the hospital for, surely not a pregnancy test, I will assume you went for other illness or injury ?

But yes if you have periods even infrequent you can get pregnant.

I would advise seriously not having sex till you educate yourself on sex and pregnancy
Had you done any home pregnancy tests before going to hospital.

Have you been seen by your personal doctor for why you are not having regular periods.