Sorry to hear you are having problems.
It can be exasperating that injuries take so long to improve.
But it sounds like a "go slow" approach until your return to Sweden and making a proper diagnosis is a good idea.
If you do decide to try a bike, really try to keep it to that 5 minute limit.
(After a brief warm up, the knee may actually feel much better - but you may pay for it the next day if you push it too much.)
The initial goal in rehab is just to get the joint moving through a normal range of motion.
There is no attempt at first to gain strength - that much stress unfortunately leads to more tendonitis.
The length of time and tension on the bike should be very gradually increased so the muscles/tendons can accomadate the increase in stress.
The reason bike exercise is usually well tolerated by the knee is that the knee is not bearing the body's weight.
But increase the tension and revs/minute too much and you can experience worse problems.
[Just do a quick google search on cycling and knee tendonitis to see how many cyclists suffer from knee tendonitis from over doing it.]
Lefty 5 has it right that knee tendonits can be caused from muscle imbalances/relative weakness of muscles in the leg or even up above the hip area. An overall strengthening program of the legs, core and muscles that connect the legs to the core is often the most effective way of preventing a recurrence. (And the squat may be the single best exercise for that - but only after you make significant progress from where you are.)
(Let us know how you are doing.)