Thank you for your question. Sometimes a dua is not answered as what we think is good for us is not in the greater scheme of things. In the same way as your child may ask you for something repetitively, but you may not give it to them as you know that it is not good for them, so too God’s Wisdom dictates which duas are granted and which are not. What is certain however, is that your duas are accepted when they fulfil the conditions of dua and the reward for those duas await you in the next life.
Also for some duas 6 years is not too long, so doing give up. There are people that have made duas for that time or much longer, and their wishes are granted later. Either way put it in God’s Hands as He knows what is best.
May you always be successful, may your duas be accepted and may you come to submit to the Wisdom of God.