You may be doing too many intervals, though that depends on the intensity. when I was developing training plans for cross-country athletes (at the national & international level) the rule-of-thumb was that interval training should not be more than 10% of the total per week. More than that, and you're tearing down, not allowing muscles time to re-build, and possibly building up far more lactic acid than is productive.
You need endurance (steady-state, aerobic) training in order to build the foundation for interval work.
If aerobic training gets boring, vary it: rowing machine, bike, running... All ast a steady rate around 120-140 heartbeats per minute. It can/will feel slow, but it builds what you need in order to sustain hard intervals.
Nat Brown taught and coached cross-country running and skiing for 16 years before joining the US Biathlon Team as wax technician. In 1989 he switched to the US Cross-Country team. He was the first American to take over technical services for a foreign team (Slovenia) and worked also for Germany and Sweden. He has coached at 3 Olympics and 14 World Championships, edited Nordic Update for 9 years and Cross-Country Skier for 2. He has written three books on skiing and training; the latest was The Complete Guide to Cross-Country Ski Preparation (Mountaineers Books) which has gone through two editions and a Russian translation. He spends as much time as he can at his ranch in British Columbia where he most recently hosted a pre-Olympic training camp for Slovenia.