Years ago I raced for Pan-Am airlines and Trek, and then Thule and Cannondale. I have a cycling and sports medicine background. I can understand the leg issue but the breathing and air consumption issue is not cycling related....in fact your cycling should make it so that you are using air more efficiently. What you describe is you suffering from not being relaxed in the water.
Spend more time swimming and playing in a pool, lake, or ocean. Do apnea work in a pool to build comfort and confidence. And spend more time blowing bubbles.
You state that you have 50-60 dives...more important is how many hours do you have underwater blowing bubbles? If you do 2 x 20min dives in a day, that is relevant experience but it is not the same as 2 x 40 minute dives in a day. It is relevant to how much time do you have in the water managing your buoyancy, your trim, and how you locomote. Number of dives is not really a good indication of experience, especially with new divers...one can dive 100 times or one can do 1 dive 100 times...there is a difference regarding experience gained.
I can recommend that you should stop worrying about how cycling is affecting your diving, in fact stop worrying about everything. Just dive and be in the moment. Don't take pictures or video, don;t carry extra gear, just be underwater and hang with the intent of moving your body as little as possible. Focus on relaxing and being comfortable.
I was working with a student last thursday night, before getting in the water she complained that her mask keeps leaking and asked what she could do about. My first suggestion was to not make the strap so tight as it compresses the skirt of the mask causing it to leak more not less. When the session ended she complained her mask was still leaking, after spending an hour with her I told her that her mask will continue to leak because she is uncomfortable in the water and generally tense. I told her that when she is able to relax the muscles in her face will relax allowing her mask to seal. When dry fitting her mask without the strap it seals fine, so the only thing I could think of was that she is contorting her face due to muscle tension.
While some people take to SCUBA rather quickly, for others it just takes time. Surviving underwater is not natural for humans, so even though we have a cylinder filled with air on back there is still some cognitive dissonance whether we are conscious of it our not...it takes time, less for some and more for others, for our brains to accept that we will be ok for the duration we plan to be below the surface, and allow our bodies to relax. As your skills and confidence improve your brain will more readily acclimate and the easier it will be for you to relax. When this happens your breathing will be more efficient and your air consumption will reduce.
Find a club or a partner to do apnea work with (doing it alone is dangerous), spend more time in the water, and perhaps take a peak buoyancy class. First thing to work on along the way is to get your weighting correct....as others have mentioned, many instructors overweight their students and sometimes it is a long time after receiving one's initial certification card that the lightbulb comes on and one realizes that they are toting around too much lead.
I hope this helps. Good luck.
-Z