Periods can  be delayed not only due to pregnancy but also other factors like stress and anxiety, etc. Try a pregnancy test if you're concerned.. if the test is negative then visit a gynec for irregular periods problem.

Ascites is a condition in which fluid builds up in your abdomen, leading to swelling. In this case, your body felt under pressure, which was the prime reason for both hypotension and anorexia. They can be triggers for periods. Therefore, it will be efficient for a doctor to see you first before discovering changes in your ascites and periods. 

Your chances of getting pregnant a few days before your menstrual cycle would be low but not impossible. Ovulation mostly occurs in the middle of the menstrual cycle, and the most fertile window for conception is a few days before and after ovulation. 

A pelvic lump is a surgical emergency, and you should not wait to visit a healthcare provider for appropriate medical examination. These kinds of masses may be caused by different conditions such as an ovarian cyst, uterus nodular formation or even cancer. I suggest that you seek medical advice from an OB/GYN doctor for further examination, and treatment if necessary.