Pumping to check your milk production is not the correct or ideal way to know how much you are making. The type of breastpump, technique of pumping, frequency of pumping can all make a difference.
If you are bottle feeding the formula that could be one reason that you are having sore nipples and are not producing as much as your baby needs.
If you give more than 30ml formula per feed you will be predominantly formula feeding with hardly any Breastfeeding
I would recommend you to see a Lactation Consultant at your nearest Cloudnine Hospital to check the baby's latch and assess your milk supply and need of providing formula. If required supplements can be provided to boost the milk supply.