At the risk of sounding like a crazy hippy, herbal, occupy person:
There is an herb available in tincture form called Boneset also know as Thoroughwort.
(Eupatorium perfoliatum). Available from the vendor Herb Pharm.
Take a 1 or 2 droppers full of this stuff with some water and then take the hottest bath your 'nads can stand. (I actually use a sauna). Go directly to bed, wrap up in warm blankets and then sweat all night long. You may find you wake up fine.?.
I was told about this method years ago and tried it when I felt a cold coming on. Killed it.
I have used this every time I have felt a cold coming on for over 10 years and only once did it fail.
Every person I have turned on to this method have had great results.
Hopefully for you it will work with a persistent cold.