I agree with Resilient_Mimi.
It is probably allergies. I would suggest that you try sinus rinses along with the antihistamine. Also, keep doors and windows closed as much as possible. If you have central air conditioning, running the fan continuously to filter the air would also help.
Let us know how you do and if you would like more suggestions. There are many life style changes that can benefit allergy control.
Another possibility is GERD. GERD can reach sinuses causing drainage and cough. If treating allergies doesn't help, talk to your doctor about treating GERD.
Take care and God bless.
Do you have sinus drainage? This could be where the secretions are coming from. That would also tickle your throat and make you have to cough. The fact that it is clear is great, that means no infection. Try taking an anti-histamine and see if this helps. Good luck! n May GOD BLESS!