What is going on with my coolant tank and water in it? I am absolutely sick of car's failing on me, please help me

Hi, please help

I am absolutely sick of it, of my cars letting me down through no fault of my own, I often feel like getting rid of my car and never getting another, I have had SERIOUSLY BAD LUCK with each of my 4 cars, I actually feel sick.

I live on a reasonable income but I feel the strain having to pay for repair after repair, week after week on car after car and I am very angry about it and upset.

current car, 2006 1.8 TDCI Sport, had around 9 months now, spent around £1,200 on it and that is not including paying for the head gasket that I was told was gone 2 days after buying the car, garage were paid £850 for HG job but later several mechanics from elsewhere told me looks like waterpump only was done, they even refused to give a receipt and make up an excuse

Since then every other week almost it has been repair after repair, honestly non stop. Car keeps trying to catch me out and has at times overheated and at other times would have overheated had I not discovered leaking water hoses.

Most recently I notice a trail of water behind car, discovered was the expansion tank was faulty so I got a used one from car yard,

However, I notice when I check water In expansion tank when it is hot the level is low, but when the car engine is cold the water in tank is higher (despite the fact water should be higher when hot as it expands ) despite this I notice that even when cold the water level seems to be dropping after several days, today it was below minimum.

We can't find any leaks after briefly looking over it today, several hoses have been replaced and expansion bottle was replaced too.

Just wondering why the water in the expansion tank is lower than it shows when the engine is cold as then it looks higher than hot ??

Please try and answer several questions here, I have a lot going on in life at the moment and this issue with my car is upsetting me very much and putting me in a depressing mood.

thanks