@Cybil62....I'm writing because it seems to me that you are still having problems with your knee as a result of overdoing things. In another member's thread, you indicated that your walk 5 miles 3-4 times a week with "no problem." Yet you also indicate that your ROM is about 90 where it's been for quite a while and you cannot do rotations on a stationary bike. You also say your knee is stiff a lot of the time.
I have some advice for you that I hope you will try for at least a couple of months.
First, stop walking those distances. Completely stop. Even though you may not feel pain when you do it, it's clearly irritating your knee to the point that you're still swollen (that's what the tightness indicates). Most of the time when you exercise, you don't see or feel the negative results until hours or even days later, so do not use how you feel when you're walking as a measure of whether it's too much or not. Because you are having these problems, I'd confine walking to what you do for activities of daily living and only that. If you must walk outside, make sure it's on a flat surface and only walk for a total of 20 minutes and not a fast walk. Allow yourself walks like this ONLY if you can do it with normal gait motion (no stiff leg and no limping).
With your current ROM, I'm wondering how you are walking. I'm sure you're not using any aids, so what is your gait like? Is it a normal stride with your leg bending and extending normally? I have a feeling it is not and that is very, very bad for you to be going distances with an altered gait. I suggest you make one appointment with a therapist who is qualified to evaluate your gait. Normally people in recovery walk around the house and do turns on the stationary bike early in recovery using a walker as support until they can achieve an normal heel-roll-to-toe gait. Then they start walking without the walker for short distances. From your history, it appears to me you tried to ditch all aids way too early before you had that normal gait. This can result in an improper gait with either a stiffened leg or a limp. Either of these situations will cause more stress to your leg and give you the swelling you're talking about.
As for the bicycle, if your ROM is 90 degrees, you should be able to use it as an exercise tool. Bikes are excellent because you can control the amount of motion completely. Be sure to adjust the seat all the way up or back so you don't need to bend as much to get a full rotation. You can always change the seat setting later as your get more ROM. If even at the highest setting you still cannot do a full rotation, then just rock the pedals back and forth for no more than 5 minutes. Be sure not to overdo this exercise either. It's more for stretch than anything. As you go back and forth eventually you'll find yourself going all the way around. It might take a few days or a week or more but it will come. You might even have to lift your hip on the seat slightly. But you'll do it. Go slow and this will help you.
In reading your entire thread, I can see you have people in your life who are trying to offer help. Ignore them. They aren't you. They haven't had knee replacements. They are not medical professionals. And they don't know what works for this surgery. Just smile and say thanks for caring and go about your business.
You must keep at this slower pace for months. Your other medical conditions such as fibromyalgia mean that you need to take things slower than others may. You've not done that and it's holding you back. If you get frustrated, come here and vent. That's what we're here for and we'll help you through a challenge. But please do stop trying to push your knee so hard.