I would have blood tests redone to see what your actual hormone levels are like. Did the GP do a day 2 test; if so did he compare the LH result against that of FSH. If that was not done then the test is meaningless.
A lack of regular periods can indicate that ovulation is not happening regularly. Some GPs are not clued up very well on such issues, you will need to be persistant in order to get answers.
BTW any test result done over six months ago should be discounted; you need up to date test results. As your periods are irregular the blood tests can be done according to calendar days.
Irregular periods are often caused by hormonal imbalances; your thyroid hormones should be checked out properly as well as a condition called polycystic ovaries (see day 2 test above).
Ovulation does not always occur two weeks before the start of the next period. It is quite possible to have periods without ovulating.