Girls, hi! Question for moms...please don't throw stones at me, it's my…

Girls, hi! Question for moms...please don't throw stones at me, it's my first baby, I haven't quite settled in yet ?? Such a question...during breastfeeding, the baby sucks well for the first 15 minutes, then starts kicking legs, getting fussy, the breast throws up, then takes again, I get nervous too and cry about it. In the maternity ward, this didn't happen, it started literally three days ago. They say maybe he isn't getting rear milk, but how do you make it so that it comes? I don't understand (the baby also became very frequent crying and really hard, four times a day maybe, is that normal already?) I don'