Lack of Grasping of the Object of Meditation

I asked a question previously about the object of meditation being faint. Perhaps I'd like to reformulate my question more specifically as I still encounter these kinds of problems, and I will provide the sensations I experience. When trying to meditate on the breath at the aperture of the nostrils, the breath is not present and cannot be felt, no matter how much I try to arouse attention. It could only be slightly felt at the level of the abdomen. When I try to visualize any object, this object is usually extremely faint and transparent almost. I have the impression my mental agitation is feeble, but also that the clarity of my mind is very dull. I'm wondering what could be the causes of this. Is it a too weak concentration? Too weak mindfulness? Is it a kind of lethargy and dullness? How can I remedy to this? Of the possible solutions I've read about I understand arousing attention (which I have difficulty doing), applying certain antidotes as the perception of light or enlivening the mind, or perhaps some other solution I don't know about. Perhaps changing the object? I'm actually unsure of any of these solutions. Greatest thanks.