Regarding doing 30 minutes on an exercise bike, that's is terrific!
It's always good to start any cardio activity in small amounts the first few weeks. Like the first day you get on the bike (or go for a fit-walk), do 5 to 10 minutes, then the same the next day. Then the next week, do 15 minutes at day. Then the week after that, you will find that 20 or 25 isn't so bad. Your small successes will make you proud and motivated!
You can avoid boredom by splitting your cardio workout into two or three activities. I sometimes start by doing 10 minutes on the bike, then switching to an exercise tape for 15 minutes, then finishing by going outside for a fit-walk. This method also involves more of your body parts, and thus, burns more calories!
My friend dragged me out for a fit-walk this morning. Her route took ONE HOUR! Almost killed my feet! But, I'm still standing, and looking forward to my weights workout tomorrow morning.
Success builds more success. Keep with it!