Why do I keep losing power when driving

Have you scanned the engine computer for trouble codes? That would be the first step, to see if the car can tell you what's wrong. Here in the US, most auto parts stores will scan your car for free and give you a list of any codes found. Alternatively, you can buy very inexpensive OBD-II scanners from places like Amazon, eBay and AliExpress; some of them are under $10.

I had a similar situation happen to me on my VW New Beetle; it turned out to be the Mass Air Flow (MAF) sensor. You can test that theory by simply unplugging the MAF and seeing if the problem goes away. Doing so will, however, turn on your Check Engine light so you'll have to be ready to reset it after you're finished testing. A bad MAF will give bad airflow information to the engine computer making it put out the wrong mixture of air and fuel. When you unplug the MAF, the computer defaults to preprogrammed settings that won't give as good a mixture as with the MAF, but allows the car to run fine for the most part.

So go get those trouble codes (AKA DTCs) and let us know what you find.