Should I be worried?

Hi Ladies,
My son is 9 weeks old and has a checkup on Monday with the doctor so I will be running this by him on Monday - but anyway, the last few days he's been spitting up quite a lot of his milk and I'm not sure why. I haven't changed formula or water supply or anything like that so not sure why the sudden change. He's spitting up so much of his milk that I'm concerned he's not keeping enough down.
His BM's have been runnier too.
He is his usual happy self and isn't crying or seeming to be sick or in distress so I'm just at a loss.
Any ideas? I'm a first time mummy so I appreciate any help!

    my girl started spitting up a lot between 2-3 months too. My doctor said 2 things. First, what seems like a cup of spit up is usually less then a tablespoon, it isn't as much as it seems. Second, babies can spit up a lot before a growth spurt because they're trying to eat more food but their stomach isn't big enough to hold it all.

    If he's fussy after eating or seems to be in discomfort while spitting up then it could be a digestive issue. Runny poops can happen for a lot of reasons and most of them aren't anything to worry about. Relax and keep burp clothes nearby!
    About Lis Outland
    Current: Selma, North Carolina
    Birth: December 31
    On since: Jan 11, 2014
    I'm the Mummy of a very beautiful little boy named Jayson. He and his daddy are my world. I'm an Aussie gal living in the USA.