[Typo3-shop] basket

[Eric Vlemmings]

I'm starting to get a nervous brake down. I don't know or understand what 
I'm missing,

I have 5 products and in my basket it shows only 2.
and if I have product 1 and 3 in the basket and I go back to my shop and 
order also product 4, then suddenly it's kicks out number 3 and I only have 
product 1 and 4 in my basket?

What's going wrong here?

please help.