Hi,
We are married for a few years.. the favourite posture is me over her, with left leg over hers and my right leg between her legs.

We have adequate foreplay but what is happening, I am not penetrating - it seems that I just enter and move sideways or around the entrance... not really going in.

One way around is that I move in with my both legs below hers.. but then the Vagina seems to be way down.. and I am unable to exert the pressure to move in ( I can do that when I put my left leg over hers).

Any tips and time is running out for us, in terms of having a child

Any tips and time is running out for us, in terms of having a child
Change position then if it's causing THAT much of an issue, it's not a contortionist tryout after all..
There's a huge range of alternative to try out there and sometimes the simplest is the best..

Has this always been an issue or is this a recently developing problem? Are there major differences in height and/or weight between you or physical obstacles that limits your options?

Why is time running out for you to have a child? Does your wife want a child or is she concerned about becoming pregnant?

Are you certain that 'foreplay' is 'adequate' for your wife? For females, arousal begins long before taking your clothes off.

Is that a good position for her? It doesn't sound like it. Along with trying other positions, you might try using a pillow or folded towel to raise her hips.

Have you considered her over you? It changes the angle a good bit.

Let me get this right... you've been married a couple of years and you have NEVER been able to penitrate her? Yet you have a favorite position? Sorry but reading this thread that's what I see.

If that's correct... why haven't you been to see a gynecologist about it?