I'm on claritin (loratadine) D and flonase, but getting little relief/sleep. Is it okay to also take either theraflu nightime sever cold and cough or nyquil coldflu?

Yes, but. Only take either, the theraflu or the nyquil, not both, and if you do, please drop the evening/night dose of the claritin (loratadine) d, till you see your doctor, read the labels carefully, might cause sedation, so don't drive or operate machinery, good luck.