OK if you last had SEX on 1st January you will be at least however many weeks have already gone this year aprox 18wks-20wks or more,
you should be able to notice you cervix is way above your pelvis bone and proberly have a noticeable bump even if it is small,
I would suggeust you go See the Doctor ASAP, especially if you are certin of the last time you had sex, as you would be almost half way into the pregnancy andreally due for a scan anyway,
Some OB clinics and Dr's have their own ultrasound machines so they could do a scan right then to see whats what
why has it taken so long to suspect somethings up