6 week old constipated 😫

April
My 6 week old has been constipated for about two weeks now with the occasional bowel movement only with help (suppository or enema) from urgent care visits. We have a doctors appointment this week but I just wanna know if any one else has had this problem? 
I'm giving him half and half Brest milk (pumping) / formula. My milk supply is seriously depleting so I am having to give him more formula 😕 what kind of formula has helped with constipation or other natural ways to help him go on his own? He is currently drinking Gerber good start soothe