Yes, you seem to have an infection, probably a case of food poisoning.
The cycles being late might just be a coincidence but I would recommend you to take a urine pregnancy test for the next week to make sure that you are not pregnant. A pregnancy test takes about 15 days to be positive from the day of fertilization. The fever with vomiting are signs of an intestinal infection and probably has to do with something you ate recently .Mayonnaise and heating pre-cooked food has been shown to be classically associated with food poisoning, and I would suggest you to keep away from them for a while.
I would recommend the following things.
1) Start a course of oral antibiotic Tab. Ciprofloxacin 500mg and Tab. Ornidazole 500 mg twice a day for 1 week. Alcohol should not be consumed during the period of treatment with ornidazole as it may cause severe side effects.
2) If the fever subsides and you still continue to experience nausea and vomiting. I would recommend Tab. Antivert once day. It might cause dry mouth and sedation as side effects, so do not drive after taking the medication.
3) Drink lots of fluids to replenish the lost water due to vomiting. It is recommended that you mix a sachet of E water due to vomitting.cation.
tting t with ornidazole as it may cause severe side lectral to 250 ml of water and drink it in a day.
4) It is important to have a healthy diet to improve your immune system and also to maintain a good routine of exercise.
If the UPT (Urine pregnancy test) is positive in another week, consult a Gynecologist for further management immediately.