formula fed 3mo old having poo issues

My daughter is 14wks old today and currently drinks similac sensitive. She didn't go poo for 1.5 days when we first switched her over from bm, but since then had been going once a day. Started having issues again recently. Last time she had a bowel movement was last Wednesday, and she seemed to be upset passing it (turned bright red, whiney, cried a little) then she didn't go for 4 days. Last night she went, but it was a vey small amount (but not hard in texture) then this morning she went again but it was more formed ( not small pellets like they say with constipation, just one formed piece that was still a bit mushy)