Ritalin For Cfs And Tolerance

I'm been suffering from CFS for years now. The condition makes me suffer all through the day for being tired, and also hurt my professional and personal life.

Recently (3-4 months ago) I have started to take Ritalin. It worked magic. After taking it I wasn't tired at all. Every aspect of my life has improved since then.

Yet, in the past few weeks it seems like it's effect has been wearing off. I used to take combinations of Concerta and LA, ranging between 36mg Concerta to 80mg LA (40 twice a day).
I am very worried that I might be building up a tolerance for the substance, and that it would not be as effective as it was because of this.

I know it's not totally conventional to treat CFS with ritalin, but it has been very efficient for me, and not only stopped me from suffering, it has also enabled me to become more successful.

I have taken a 2 day "holiday", but I still feel the same dosage is not as strong as it once was.

Additional facts:
- the past month or so I've only been taking LA (40-80 a day), and not concerta... which could attest to something.
- I never take 2 pills at once... if I take two, it is separated by 4-8 hours.
- It seems that it's relatively short acting in my case. Concerta lasts about 7-8 hours and LA 5-6. Also, it takes me more time to feel the effect - concerta = an hour. LA = about two hours.

I would really appreciate your input, any input (questions, advices, information, personal experience...), about this issue.