Are the tips of the grass jagged? i.e., is it a ragged cut? Your mower blade could simply need a sharpening. It may not have shown up before and the dry conditions could be highlighting it.
I would shy away from mixing fertilizers, that just sounds like a slippery slope to me. However, if it was going to get fertilizer burn, I think it would have happened by now - probably soon after you applied it. Do you know if it was a slow release fertilizer?
Check your mower blade first. Give the lawn a deep watering as well. If it's been two months, you're actually about due for the next feeding, assuming you're using a slow release product.