Thanks for writing to DoctorSpring.com with your health concern.
It could be a vaginal infection that can lead to uterine infection ( endometritis) leading to spotting.
Stress, anxiety, weight gain, hormonal medications, late nights, erratic eating habits, smoking, drinking - all can lead to irregular spotting instead of a formal period.
Dysfunction of thyroid hormones or PCOD - polycystic ovarian disease could be possible.
Rarely, an ectopic pregnancy can lead to negative pregnancy tests and spotting.
Please consult a gynaecologist and have a complete internal evaluation - per vaginum and per speculum.
Next a pelvic ultrasound scan should be done.
Also, hormonal levels - FSH, LH, TSH, Prolactin, OGTT.
In view of your unsuccessful attempt to conceive for over a year now, this workup is all the more essential.
In addition, a cycle of follicular monitoring should be done to check if you are ovulating as required.
All the best
Hope this helps, Please feel free to discuss further.