No period for 4 months then 3 weeks of spotting?

[Puzzles10]

As title says - I last had a proper period at the beginning of November (never been regular, but this is the longest cycle I've had before), and then for nearly 3 weeks I have been spotting. Some days barely anything, some days a bit clotty but not enough to be a period. Dark brown colour. I just wondered if anyone has any idea what could be causing this? I had a blood test about a month ago and LH came back borderline slightly raised so the doctors are going to do another blood test again to see if it is still raised. I also had an ultrasound a year ago which came back normal. I'm 22 and worried about my fertility..