Nopal and random/easy bruises

Don't know about Nopal, however in response to your question about blood thinners - yes. By definition, thinners reduce clotting speed and therefore you bleed more easily. Subject to the quantity/type of thinner you take, a simple knock you would not notice can result in a small bleed ie a bruise.

If you bruise too easily this should be checked out. Some drugs (and I assume, albeit far less likely, some natural thinners) can result in over thinning.