Could you recommend a prayer for a woman who is trying to get pregnenat with no luck for few years?

I’m not sure which books you have available. There are some (e.g. Aneini) which have different kinds of prayers for different kinds of people/ circumstances/ occasions.

Assuming you have only the basic texts, I would suggest reading the Haftorah for first day Rosh Hashana (which is the beginning of the book of Samuel) after lighting candles on Friday night. I believe that some prayer books also have a special prayer to be said by the woman of the house after lighting candles, which is probably appropriate.

Prayer is extremely important (as we see from the Torah – all the matriarchs, with the exception of Leah, had no children at first – G-d wanted them to pray because the prayers of the righteous are so dear to him). Also, ask others to pray for you. They should use your name and your mother’s name.

Make sure (and I assume you have done this already) that you get the best possible medical treatment. If you have tried one doctor with no success, try another one. The Talmud says that not every doctor has the merit to heal every person.

Also, try to keep the laws of family purity. This is very important for a woman who wants to get pregnant (apart from the possible medical benefits, there are many spiritual benefits mentioned in the Talmud).
With blessings for all our prayers to be answered speedily. As Eli answered to Channah (Shmuel 1; 17) “May the G-d of Israel grant the request you have made of Him”.

Rabbi David Sedley