Hi Torty, I feel your pain. I'm Type I for 25 years and also have severe nasal allergies. I do not have high blood pressure but my docs don't want me to take anything with a decongestant because they say research shows long term use causes high blood pressure. Several years ago I was suffering just like you and resorting to Claritin D because it was the only thing that helped - I knew it wasn't good for me but I had to be able to work.
I would suggest that you go to an ENT doc. There are different things they can give you to try safely. I ended up at an ENT when I had a severe sinus infection that would not clear after rounds of potent antibiotics. Long story short they had to do sinus surgery to clear the infection but since then I have seen the ENT regularly and been problem free using only the regular claritin (not the D) and a daily nasal spray prescribed by the ENT.
Also try using a neti pot or something similar to flush your sinuses - you can buy it at the pharmacy. The ENT told me to try this and as horrible as it sounds, it really does make you feel better. Make sure you use distilled water though, not tap water because there are amoebas in tap water that are safe to drink but not to flush your sinuses with.
I hope you find something to make you feel better. Please ask a doctor what to use though. The Claritin D isn't your best option with your blood pressure history. Take care.