Just started to do a similiar thing, started 4 weeks ago.
Cycle to work - 12miles - Lunchtime run 5-8miles - Cycle home.
Only run 3 weeks days (mon, wed, fri) also Swim 2 mornings (wed, Thur) - Wednesday is a killer day!!!
Now this was a very significant increase in training for me ( up from just around 45miles running a week and nothing else) and the first 2 weeks were exhausting. But now at the end of the 4th week I feel fantastic and have even introduced some weight training to it.
I think it takes a little time for your body to adjust to the 'shock' of the extra work and as long as you train easy at the start and eat well it does become normal. Preperation the night before is vital.
Problems - 1 rucksack on bike and one dropped off for me by my wife, tonnes of washing. Can't seem to carry enough food to see me through the day, average about 2000calorie burn a day. Early mornings are stil a struggle. My eyes don't stay open much past 10pm(well 9pm really if you count the 'nodding' in the chair). My shower gel and deodrant bill has gone up !! but I am very clean !!
Weight loss has become a battle hence the weght training but not a real issue. I would say go for it, give your self a few weeks to adjust and the benifits will amaze you.
Improvements in my running have been staggering, I would plod along at about 8min miles for the medium to long runs but in the last week this has dropped to 7.30 pace with very little noticeable effort.
Good luck and stick with it cos it gets easier..............