I took melatonin and still cannot sleep can i take squill as well?

I think you mean Zzzquil. It is ok to take Zzzquil with melatonin. Also melation comes in many different doses - 1mg, 2,mg 3 mg, 5 mg and 10 mg. The 5 mg should be used for those not responsive to lower doses. If you are having trouble sleeping with it you need also to make sure you are not drinking coffee or eating chocolate n the afternoon or evening (which can affect your sleep).