I'm not an experienced rider, but your symptoms trigger my brain to think "electrolyte issues". February it is cooler. Now it is hotter. You are expending alot more fluid via sweat, etc. If you are low on sodium, potassium, etc., you will feel it, for sure. That is why, maybe, your body is telling you "Don't ride! Fix me!" Are you drinking something other than plain water before you start your ride and during your ride and recover from your ride?