I’m concerned about a delayed period.

I had my period until around July 26 and had brief unprotected penetration/a few strokes on July 30–31, with no ejaculation inside or near the vagina. My cycles generally range from 28–35 days (I have had 34–35-day cycles in the past). This month I’ve been travelling right after mu period, ill with fever, had chills, food poisoning and fatigue, and I’ve also been under significant stress because of a skin condition. My period was expected around August 20(taking cycle day 28), but I’m now around cycle day 36. I took three home pregnancy tests: August 24 afternoon – negative, August 24 evening – negative, and August 27 at 4:30 AM with first-morning urine – negative. I am concerned about pregnancy...i am having pms symptoms like stomach ache and lower belly cramps but no period...how long to wait or what to do...please help me