Highly unlikely your diet is causing the problems otherwise you’d have seen it long before now.
What happened most likely, is you damanged your muscle and ignored it. Or it didn’t hurt enough for you to pay it much mind.
I have hurt my arm picking up a ten pound weight. And I can curl over 100 pounds with one hand.
If you’re legs feel stiff and tight there’s a reason for it and it’s probably you hurt yourself. You can have small tears. So my adivce is stop it, NOW.
Start stretching your legs. Go to the library and get some books on healing and stretching and yoga postures. They really help you. Do this first before running, actually you need to lay off the running for a bit. You can do things like swim, which would be the first choice or use the stationary bike.
Cold is used for healing but warm actually makes you feel better, but cold is better for any type injury. So what you may want to do is switch off cold compress, followed by a heating pad or hot water bottle.
Whatever you do, listen to your body. If it hurts something’s wrong so you need to stop what you’re doing an re-evalutate your workout routine.
Sometimes you DO need a break, take a week off. Or just do weights. But if you can get to a pool do that. Swimming is great, so long as you SWIM and don’t just float around