While just about possible, this is unlikely in the extreme. For a woman not lactating or breast-feeding, fertility can in some cases return a few weeks after giving birth, but for most women it takes several months, and 14 months for the menstrual cycle to return to normal.There is just time for Cleopatra to have borne two children. Diodorus says she had given birth a few days before Philip's death. That gives a conception date of January 336 BC, perhaps 6 weeks after she could have given birth in DEcember 337 BC, putting the wedding in March 337 BC.
For a woman lactating or breastfeeding, this acts as a 98% effective contraceptive for up to 6 months. After 6 months, or after a woman has had her first period since giving birth ( usually several months after - see above), breastfeeding can no longer be relied on as a contraceptive......
As Paralus says,she would have to have been incredibly fertile, and the probability is extremely low, especially if, as seems likely, she was lactating or breast-feeding.....