Well unfortunately, without a lot more detail on the changes you've made to your diet and how you go about your exercise, it is impossible to exactly pin-point where the problem is, but here are some facts and pointers to help you out.
There are three main factors here:
- Hormone levels
- Diet changes
- How you exercise
Normally, training alone doesn't cause significant increases in testosterone for there to be an effect on skin / acne, but if you are taking any supplements for this (like testosterone boosters), or happen to be going through puberty, then you may want to look into this with a doctor / dermatologist.
There are a lot of foods that you may have implemented in your new diet that can be causing acne. Dairy, for example, has had plenty of studies going back and forth as to the effects it has on acne, with a nice amount claiming certain amounts of dairy can cause it.
For more information on dietary causes, please read this article full of information and advice. It will help you spot any new foods you may have introduced into your diet.
How you Exercise
Just like the dairy studies, plenty of people have gone back and forth with studies and evidence on sweating clogging up your pores.
The main principle behind this is that as you sweat, the sweat brings dirt and oils from the surface of your skin into your pores for them to get clogged.
This article gives more information on how sweat affects acne.
And from personal experience, sweating caused me to develop some acne when I started training, so if this is the cause of your acne, you need to look at a few things:
- How soon after your exercise do you shower? Leaving the sweat on your face for a prolonged amount of time isn't recommended, and you should wash your face as soon as you finish. On the counter-side of this, do not wash your face too often, as dry skin can also give you skin issues / acne.
- While exercising, make sure you are using a clean towel free of dirt to dry your face. Do not reuse towels before washing them between workouts. The dirt and oil left on a towel can be detrimental in preventing acne developing when you sweat.
- When showering, try using an exfoliating face wash that will assist you in properly deep cleaning your pores after a workout. Any product you use should be tested first, and used sparingly.
For more info on face washing, please check out this page for good tips on how to, and also for further tips on products.
So in Conclusion:
Your acne can be caused by a plethora of changes you can be making to your body through hormones, diet, and exercise. But pinpointing the issue from the tips above and reading the cited material will help you make the changes needed to prevent it and finding the cause.