If he ejaculated in you then you should be cautious about chances of pregnancy.The home pregnancy test may be negative in early cases and in that case it should be repeated after a week.The blood hcg test is more sensitive
The pain during sex, lower abdomen pain, irregular periods
may also be due to the genital infection
and that should be ruled out.You should have the pap smear
, blood test
and physical examination done by gynaecologist/doctor to know the underlying etiology.
The treatment depends on the underlying cause.