Hi,
The BASED on the description it seems your periods are irregular, here are some causes for irregular period that has inset recently.
1)
STRESS OR Over-exercise
2) EXCESS OF COFFEE,
3) Significant weight gain or loss
4) Excessive alcohol use /
SMOKING,
5) Poor nutrition (or a diet too high in carbohydrates)
6)
PCOS.
Based on the information it seems like more of stress related / excess of caffeine, may be cause of the delay in period .
--------------------------------------------------------------------------------------------------------------------------------Now lets deal with question about
PREGNANCY :
"The pregnancy test is negative is huge indication that your NOT PREGNANT "
Following is information which can put some light and help you come out of thinking you may be pregnant if we understand about OVULATION & PREGNANCY
The process know as "OVULATION" is when the female egg releases from OVARY, this occurs roughly between the 14 th -19 th day after the menstrual cycle (end of bleeding ), pregnancy means the meet in of the man's SPERM to the female's OVA- both have half genes which need to get together in order to form a complete structure, so the best possibility for the pregnancy is if the intercourse has occurred during those five days, other time their is no OVA present to meet the sperms hence no possibility of getting pregnant.