Clarity During Meditation

I'm wondering about clarity within meditation. I seem to have diminished greatly the agitation I experience, but there is a degree of mental sinking, of mental tiredness which I have a hard time eliminating. This tiredness seemingly makes the meditation session a meditation on the feeling of lethargy and laxity, and I am having a really really hard time ridding myself of this dullness. I've tried antidotes of uplifting thoughts, I've tried having equanimity towards the sensations, and remaining with them. I've tried tightening the breath, focusing sensations more closely on a specific area close to the nostrils. Yet, I've not managed to rid myself of this dullness, and I wonder if I should keep meditating while it is within my mindstream. Any advice would be appreciated.