After changing the oil a month or so ago i began to notice white smoke puffing from the exhaust when revved (i noticed it because i started the car while standing outside of it, covered in oil). If i put a rag or a hand there it becomes wet

I think i'm losing coolant. Last time i checked the plastic reservoir near the windscreen i'm pretty certain it was over halfway between low and high. Now it's only a quarter.
The Petrol gauge swings as much as 1/8th randomly (ie. sometimes i'll look at it and its at half, sometimes i'll look at it and its just over 1/4).
When filling the petrol i have to do it very slowly otherwise the nozzle cuts out like its full (this happens at all garages).
I only got 380km out of the last tank, and i rarely see above 3000rpm (petrol light didn't come on but it was touching the empty line).
Oh god I think i'm going to cry

Any help on any of those matters would be much appreciated.