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Please get your wife examined by a Gynaecologist to see if your wife has normal vaginal opening or imperforated hymen
.If the opening is proper then try doing more fore play & if required use K-YJelly or Lubic jelly for lubrication.
Secondly please see for yourself whether you get proper hard erection which is required for penetration;if you don't get it then it will be difficult to penetrate.In such a case even you may need counselling
or treatment just in case if you do not get proper erection.