You’re really approaching the whole field of metaphysics with this one. Reading an overview of metaphysics would be the place to start, this sounds pretty dualist, dealing Berkley or Descartes would be a good place to start. You might be interested to read an overview of phenomenology too as it in part theorises how the senses play their role in building reality.

This breakdown of your statement might help you see where you’re stuck…

1)’If reality is but a mere mental construct’

2)[mental construct] ‘conveyed to my mind by my senses’’

Conclusion) ‘then, are my thoughts and mind a product of my senses’

The main contradiction arises simply from a lack of clarity of terms. If ‘reality’ is a ‘mental construct’ then what role do, and where are, these ‘senses’ that are underpinning it? How do they exist outside of reality? I suggest you define your meaning of each of these terms which might help you build your thoughts.