Tandem Feeding

To all breastfeeding moms like me, how do you handle tandem feeding? I'm currently 5 months pregnant and planning to tandem feed my 1 year and 8 months old with his sibling once I gave birth. Actually I'm having a hard time breastfeeding my toddler sometimes due to my sore nipples. I tried to offer formula milk, 2 brands already, but he always refused drinking it. And when we offer fresh milk because he eats cereals sometimes, he loves drinking it. I'd like to add also na maselan po ako magbuntis sa 1st and 2nd child ko, and my OB advised me to continue breastfeeding as long as kaya ko pa, hindi naman daw makukulangan ang baby ko sa tummy ng nutrition if I continue breastfeeding my toddler, kaso last night I experienced pregnancy cramps, tolerable naman pero ang tagal bago nawala then nakatulog na ko, si hubby na nagpatulog kay toddler. So this is my 3rd pregnancy na din. I didn't breastfed my 1st child this long like my 2nd, I think 3 or 4 months lang ako nagpa-breastfeed nun sa 1st ko then I started working again. Feel free to give me some tips how to handle this based on your experience. Thank you momshies!