Constipation. Is it normal or not?

My baby girl is 2 months and a week old, she is on both breast milk and formula 30ml 2/3 times a day. Initially I was My baby girl is 2 months and a week old, she is on both breast milk and formula 30ml 2/3 times a day. Initially I was giving her formula as a top up after every feed. Because of the low birth weight the doctor suggested giving her both breast milk and formula mi vitamin d3 1ml per day, Ossopan d 1 ml three times a day and tonoferen 0.5ml once a day. And MCT oil 4/5 drops after every feed upto 4 kg. Her birth weight is 2.2kg. After 10 days she weighs 1.9kg and now at 70th day she is 3.5 kg. For the first two months she is passing stools 4/5 times a day but from past 10 days she is passing stool once in a 4 days, her urine output is 8 to 12 times per day and also passing gas as well. She is active and playful but while passing stools she is straining too much because of hard stool. Is it normal or not? and how many days we can weight for the baby to pass the stool.