I have done tube wash in june and on 3 rd july i have iui without conceiving. why??

Nobody knows: Unfortunately nobody knows. In every normal cycle, in a woman with no infertility issues, there is only a 20% chance of getting pregnant if everything goes right. This number is far less in women with fertility issues. IUI does improve your chances but nothing, not even IVF is 100%. Don't lose hope though because just like life, sometimes it works and sometimes it doesn't.