Can anybody tell me why the income fluctuates?

If you find any problem with your income than why don't you ask directly to mylot site. My experience is always good for this site. They gives me reply of all my querry very fast. So, better your ask them and I hope that your problem will definitely solve.

I remember in the guidline I read it mentioned the reason for fluctuations in your earnings. That is, when someone else's discussions got deleted, they lose some of their earnings. In the meantime, because the whole amount of money is set, other people get extra money from the earnings they lose. So when some discussions got deleted, if you responded to that discussion, you lose money; if not, your earnings will increase. This kinda thing happens.