Hi Naomi
As one who has had knee problems ongoing for several years it doesn't sound good! As the knees swell due to inflammation caused by the RA it puts undue pressure on the soft tissues and joint lining. This in turn may cause the knee to malfunction. Often when you get the 'giving way' symptom it can be down to cartilage damage or a foreign body, perhaps a tiny fragment, an osteophyte, that has broken away and locks the joint occasionally. You may then have a period when you don't seem to have the symptom.
As knees are weight bearing it is important that it is rested, usually with the leg raised to help reduce fluid build up. Inflamed knees benefit from regular cold packs and the use of a knee splint (got mine from Boots). Tubigrip is normally only adequate for soft tissue injury and will provide only minimum support. Definitely worth using a stick or crutches for support when you are able to. Gentle movement is key to stop the knee from stiffening up.
If the problem persists it does need reporting to rheumatology who may in turn refer you to orthopoaedics for investigation. Alternatively, or in addition, you may be referred to physio ... they can offer some great exercises to strengthen the joint and surrounding tissues. At the moment I am on 12.5mg prednisolone to keep the knees in check, anything less and they just flare up again. Might be worth more steroid for you in the interim until it can be investigated.
Good luck Naomi
Lyn x