Help! New vitamins, long period

Hi all,

I started new "trying for a baby" vitamins about 3 weeks ago. I have irregular periods, usually having one every 70 days or so, so when my period started just over 1 week after taking these I thought they were helping! However....

I've now been on my period for 11 days - granted it's light now, but definitely still present! :(

Has anyone experienced this? Should I stop taking the vitamins? My OPKs have just started to darken and I'm so worried that I'll ovulate and miss our chance.

Thanks!