I'm training for a 5K and I train every other day and have been for about 2 months or so. The first day was the hardest…

I'm training for a 5K and I train every other day and have been for about 2 months or so. The first day was the hardest and it gets easier as time passes. But every time I push myself harder than before I get a bad headache. I hate it so much but without pushing myself I wouldn't have gotten to where I am today.