Try and slow things down as you approach the end!! I birthed both mine flat on my back, with DD1 I had a few grazes but DD2 popped out after only two pushes and I wasn't even swollen afterwards. The best advice I can give is that you try and avoid an epidural or other painkillers, gas is fine because you can still feel everything and you will 'know' when your perineum is at its limit and needs a few more minutes to stretch, if that makes sense? The burning sensation as baby is crowning is horrible, but just try to breathe through it knowing that it will only last a little while longer. I had a midwife telling me to keep pushing but I just knew I needed a bit more time, I held myself back (as hard as it was!) and waited until the next contraction, and with that one I just bore down a tiny bit rather than straining at it.
Once her head came out, I laid back and told the midwife to do the rest of the work (pull her shoulders out)

I've heard the perineal massage works wonders too but I didn't do it with either birth, I'm probably just lucky but trying to slow things down, and staying unmedicated (I had gas, but nothing that totally killed the sensation) in order to let me feel when my body was ready worked for me. HTH Good luck this time!