I have a head cold. i am a type 2 diebetic and i also have high blood pressure. what can i take from over-the-counter that will not have an impact on ?

Depends on symptoms: If you have no other confounding conditions or medications........If congestion is a major issue a few squirts of oxymetazoline (Afrin) up the nose should do it. This does not raise BP significanty. If aches and pains or fever are a problem acetaminophen will be fine. Cough could be treated with guafenesin / dextromethorphan.

Benadryl (diphenhydramine): Benadryl (diphenhydramine) is an older generation anti-histamine and is the best for you in your case. It will decongest you, allow you to sleep at night and not worsen BP, glucose, etc. Please note it is sedating, so take at night before bedtime/after dinner. Avoid all over the counter meds with pseudoephedrine -- raises BP as side effect because a strong vasoconstrictor.