I just wouldn't train 2 days in a row if you're body's not use to it !
If you're are shocking your system then the CNS is getting mixed signals , when starting back give it a 3day rest between workouts especially if you are over 30 !
You mentioned you are overweight by 30 pounds that's alot to shift , work hard but allow your body to recover it's hard to do when you feel good but overtraining is as bad as undertraining and in alot of cases worse

Seriously I run hard twice a week at a good pace I do one treadmill run and 1 run through the forest .
the treadmill run is too guage how fit I actually m and the forest run is for the speed and proper endurance training and sheer enjoyment .

Mix it up brother I guarentee if you work hard you will see the results but you gotta mix it up otherwise you will get bored in 3 months,platuea and then probably put on the weight .

Go easy,rest,eat well and Van xhilds is right you cant just hydrate yourself by drinking a bottle of water before a run , keep it steady all the time and dont go wild .

Take a fitness test once a month at your doctors ( they will do it properly ) ,check you pulse once a day at miday 2 hours after breakfast .

If your taining properly you pulse shoud come down by an average of 1 beat per minute per week .

It will be higher in the morning than it is at night so lunch or teatime is best depending on how long you been up .

At the moment mine is 53 when I wake but as low as 46 resting at night .,it will speed up after eating also .
the benfits of being fit are much higher than weight training without cardio .