Baby has a sore bum! Help?! ?

Our little girl is nearly 9 months and over the last three to four days she has been poohing ALOT but they tend to be two normal thick sizeable ones followed soon after by several small acidic ones (like wet farts). It is these acidic ones which have caused her really bad soreness, we are using sudo crem and bepanthen but the acidic poohs are so frequent there is no respite! She hasn't teethed yet. What is causing this? Is it normal? She has just started having very diluted squash (same one as us)