I only get my period every 4-6 months?

i started my period roughly 2 and a half years ago, and from then i've never had a regular period. for the first 4 periods i got every 6 months, and this was very unpredictable because i never knew when it was coming and this worried me. however, i had a period early January and then came again in mid-May- 4 months. I went to my doctor and she said that it's normal to have irregular periods due to all the hormonal changes in your body, and that i should wait for around another year or so and if things aren't in order by then, then she would put me on the pill. why isn't my body working regularly, and what causes the delay in period arrival? could this affect my health and fertility? thanks x