NHS Direct says that you can take the stuff that makes you feel drowsy, but not the non-drowsy stuff:
FWIW I have been having a teaspoon of local honey in my tea every day for 6 weeks and hayfever has been OK so far, fingers crossed.
The NHS Direct link is www.nhsdirect.nhs.uk/articles/article.aspx?articleId=935
... and here is an extract of what it says.
"Antihistamines are not licensed for use in pregnancy. However, the older (sedating) antihistamines (such as chlorpheniramine) are usually considered safe to take in pregnancy. You must take care when driving as they can cause drowsiness.
You can also usually use antihistamine eye-drops (use with care as some people are allergic to them). An antihistamine nasal spray can usually be used with caution during pregnancy. However, you should consult your doctor first if you are intending to use eye-drops or nasal sprays.
You should not use the newer, non-sedative antihistamines (such as terfenadine, astemizole, loratidine and cetirizine), as the safety of these medicines in pregnancy has not been established.
Decongestants
You should not take decongestant medicines or nasal decongestants unless specifically prescribed by your doctor, as there is insufficient evidence of their safety.
Corticosteroid nasal sprays
These reduce inflammation in the nose. The amount of corticosteroids in nasal sprays is small. They are generally considered safe for short-term use, as long as you use the recommended dose. Drops should be avoided as more of the medicine is absorbed into your body and so there is more risk of side effects.
Sodium Cromoglycate
Sodium Cromoglycate prevent allergic reactions in the nose and eyes. This is a non-steroid preventative medicine and is available over-the-counter (OTC) as eye drops or a nasal spray and is usually considered safe for use in pregnancy. Sodium cromoglycate is relatively short-acting, so has to be used several times a day to be effective.
Your doctor will advise you on what is safe to take and can provide medicines on prescription, which are free while you are pregnant. Your pharmacist will also be able to advise you on what is safe to take."