Taking zoloft AND adderall(adderrall) - dosage questions

[Momness]

I am a stay at home mother with three young boys.  I have been taking zoloft (100mg daily) for depression for about nine years.  The only times I was not taking zoloft is during my second and third pregnancies (and, boy, it was tough).  Zoloft has changed my life - and my family's happiness.  

Just recently I was also diagnosed with ADD.  My doc gave me adderall (adderrall) 10mg IR to try.  The first day was wonderful - I was able to slow down and focus and much of the frantic feelings I normall have were gone.  I even had a calm, "happy" feeliing, too.  Since then, I've had weekly checkups to monitor my dosage and my doctor and I have slowly worked up to 30 mg of adderall (adderrall) a day (20mg XR AM and 10 IR PM).  Since that first week I've been feeling TIRED when taking my adderall (adderrall) and don't think it's working very well anymore.

I asked my doc today at my weekly checkup if we should try to raise my adderall (adderrall) dosage, and she said that maybe we should try to lower my zoloft dosage instead - that might be what is causing my tiredness (when combined with the adderall (adderrall)).  Since I've been on 100mg daily for YEARS and it works very well for me, I'm frightened to lower my zoloft dosage.  I see Adderall (adderrall) as a drug to help me when I need it (and maybe not take it all day every day), but zoloft is something that I can't choose to take or not to take. . . .I need it on a daily basis or I notice a difference big time.

My first question is - is it really safe to take Zoloft and Adderall (adderrall) at the same time?  Secondly, how can I get the benefit of both drugs without this tiredness.  Should we decrease zoloft, increase adderall (adderrall), try another ADD med??  

I also don't understand how the two interact in my body - don't they do different things?

Thanks for any help, experiences, or insight. . . .especially from a medical professional.