Side effect of a balanced diet?

Its just because you are eating more fruit and veg - don't worry. Having peppermint tea will help, as will proactive drinks and yoghurts that promote 'healthy bacteria' in your gut. If its hurting or making you feel sicky have some pineapple, it contains enzymes that promote digestion and ease sickness. Hope this helps - good luck with the fitness regime, (as an ex-fitness instructor...make sure you are allowing your body time to recover between those runs, especially since you are returning after a long break... and ensure you are stretching afterwards).