Quads burn a lot while jogging, but heart and breathing okay?

I’ve been exercising (strength training) and eating well for a while, but I’ve just recently started implementing cardio using the C25K app on my phone. It’s 3 cardio sessions a week meant to take someone from being a couch potato to running a 5k in 8 weeks, I’ve been working up through them while doing my normal strength training the other 4 days of the week.

As the days get harder, I’m finding that my cardiovascular system really isn’t my limiting factor. Sure, my heart rate goes up when I jog, but it’s nothing extreme. Same with breathing, yeah I breathe heavier but it’s nothing I can’t handle. If those were the only aspects of cardio then I really wouldn’t hate cardio much at all haha. It’s really not bad.

My problem is my quads (sometimes calves some too, but mostly quads). They BURN like crazy when I jog. It’s brutal, the precise reason why I hate it so much.

I don’t think this is normal? Don’t most people struggle more with catching their breath and their heart rate and whatnot? Am I doing something wrong? Is there anything I can do to help lessen the burning sensation?

Any help with fixing this issue would be appreciated. I do want to make cardio more enjoyable because I know it is so beneficial for health.