Thanks for writing to DoctorSpring.com with your health concern.
As you have rightly surmised, most of your symptoms do tally with those of Endometriosis.
Now, without a laparoscopy, it is difficult to conclusively say this, unless something shows up in a pelvic ultrasound scan, which is not invasive, and often reveals stigmata of endometriosis. So why not get that done, by the way ?
Regarding the unusual bleeding that happened in the second week of December, I suspect that it is due to endometriosis indeed.
Endometriosis is characterized by irregular cycles too, and off and on spotting.
So the erratic period ( bleeding ) could have been due to endometriosis, and you anyways have a history of irregular cycles, so it does fit in. It could have been precipitated by the infection you said you have.If the pattern does not recur do not worry much.
If it does, then a polyp, or cervical erosion should be ruled out.
Taking hormonal medication for short term symptom control for your endometriosis is a good option, but it is your call.
Have a gynaecological evaluation if you have not had it in the past six months. An internal exam - per vaginum and per speculum and a pelvic ultrasound scan.
Stress, anxiety, hypothyroidism, weight gain, late nights, erratic diet and sleep, ingestion of medications that affect the hormonal axis - these are just some reasons that might cause irregular bleeding. Make sure they are ruled out too.
All the best. Please feel free to discuss further.