Knee pain and excercise, any tips??

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Hi guys,
I'm 174 lbs, 5' 5", 20 yrs, female

I've always remembered my knees hurting when i put too much weight on them my entire life, it isn't diagnosed for sure, but we think it may have something to do arthritis because I have had psoriasis my whole life and arthritis and psoriasis go hand it hand..

I just got a gym membership a couple of weeks ago, and the first 7 days i went every day straight, with little to no pain.
I would do an hour of cardio one day, and then a half hour cardio and half hour weight training the next day and switch off. And then I took a day off and then I noticed my knees hurt when I am walking, and if I'm carrying something heavy, and it hurts to lock them if I'm standing I have to keep them bent or it hurts... I have been unable to go back to the gym in 4 days now because it still is killing me the same as bad as when it started...

For cardio I do the elliptical and bicycle machine, which are both I supposed to be better for knees, so I don't know what exactly is wrong here, it's pretty discouraging at the same time because i'm finally getting results for the first time in my life since i started trying to lose weight, which has been as long as I can remember... My workout and protien rich diet has had a great week and I feel like I can do this forever, before i started at the gym i had lost 7 pounds already just with diet, and since starting there i had lost another 4 pounds. Now I'm stuck until I can work out again, the workouts aren't exhausting and I've been sleeping better than ever, now my knees are holding me back. : (

I just want to know if anyone knows any ways to get my knees to heal faster or why this is happening, I feel like after four days the pain should be gone, especially since I'm only 20 by now but it has remained at the same level,

If anyone has any tips or advice I'd greatly appreciate it.