What is wrong with my 3 week old baby?

I am feeding (actually pumping) my daughter and I do put a little cereal in her bottle becuase she spits up alot and her dr said to add 1 tsp of cereal for every 4 ounces of milk. now she's 3 week old and seems to grunt a lot like she is having trouble having a bm(she goes about once every two days) and it's normal(not hard) she does have a lt of gas which I use gas drops but she cries so much i still fel something else is wrong, I don't know what else to do, and before I take her to the dr I just wanted to see if I am the only one with this problem and is it easy to fix or do I need to see her dr? Any help would be great.