Should I ask for more money?

I on occasion work for a doctor. I used to work (half day) at the centre he's based in so I would spend half day working for him (when I was off duty) and half the day at my actual job but keeping an ear on his phone and helping him with payments, (he's only there two days a week), making sales for him, etc. It was only for five days (his receptionist only went away for a week at a time).

He paid me X amount for this.

I left the centre at the end of June, and was asked to work for him for six days earlier this month when his receptionist went on leave again.

This time I worked four full days for him, and two half days. Before remember I only worked half days.

And this time I travelled out especially to work for him. 22kms each way, in peak hour traffic. And because I had to work full days, I had to get someone in to look after my pets (I have kittens that require three times a day feedings, as well as special needs dogs).

He paid me today and it was the same amount he paid me prior. For working for an extra, longer hours on four of the days and travelling out especially to work for him.

I get that he's only there a couple of days a week however I still spent my time and petrol at his practice as per his request. I haven't earned this little per hour since I was 19.

Should I ask him for more money or just leave it but never work for him again?