I am also allergic to grass pollen.

When I lived in England I would have to put up with the misery of hay fever for about 6 weeks in the Spring.

Since I came to Spain the problem is much less than the UK because there is less rain.
However if there has been a lot of rain in April which encourages grass growth then I will have a week or so of hay fever.

When the hot sun comes in June and dries up all the grass it ends the problem.

I have found that if the wind is blowing in off the sea I don't get hay fever if I am at the coast.

A few days ago I was suffering and I took some of my friend's antihistamines which gave me a horrible lethargy and drowsiness.

The next day I went to the (farmacia) chemist and they recommended Flonase (now called Rhinovin)
The cost is about 14 euros. You don't need a prescription. 

Aparently they are 4th generation antihistamines.

They stopped my hayfever and gave no drowsiness so I am very happy.

Many people in Spain are allergic to olive pollen and also pine pollen.

It would be terrible if you came on holiday to Spain in June to discover that you are allergic to olive pollen, it would be a nightmare.

If this happens get straight down to the farmacia and get some  Flonase (now called Rhinovin)

Farmacias in Spain are normally very helpful.

The Farmacias are now very strict and they won't give you anything which needs a prescription. 

BTW: If you need a prescription for a fairly low level medicine look on internet and get an online private doctor to give you a prescription.