Questions Late Period

Is it possible to be pregnant? 16 days late. Last time I had sex with my partner (pull out method) was March 5th. I ended up getting sick and went to the ER on March 13. I was negative for HCG test, after completing a CBC (I had a viral infection). My period came for 5 days regular bleeding, week of the 20th. I am 16 days late is it still possible to be pregnant. No sore breasts. Just PMS symptoms (agitation/emotional) and lower back pain.