Feeling sleepy on Modafinil (effect inversion, tolerance, after two years)

I've been using Modafinil (Modalert) for the greater part of the last two years. I felt all I expected of it and the benefits far surpassed other nootropics tried - intense wakefulness, fluidity of thought, improved working memory and a general zest for life. I've experienced the usual tolerance where it doesn't appear to do anything but was able to reset it to some degree by a break over the weekend. The regimen I followed went roughly as below.

• 50mg (occasionally 100) on weekdays (x5)
• Break on weekends (x2)

Lately however (past couple of months), immediately after dosing - I experience an almost overwhelming sleepiness/drowsiness irrespective of how long (or well) I slept the previous night. I've tried the following (as read in other threads) with very limited success.

• Milk thistle
• Bioperine/Curcumin
• Grape seed extract
• Break for 4 days (haven't managed any longer)

One approach that did help was dosing 10-20mg of Noopept which reduces (but doesn't eliminate) the sleepiness and I've currently resorted to using Noopept along with Modafinil. The days I don't take Modafinil, I don't feel the sleepiness but I miss the other benefits.

I'm quite a noob in this field (but Modafinil had such a positive effect on almost everything for me, I find it hard to give up) and would greatly appreciate any thoughts/suggestions anyone might have.

tl;dr: Modafinil started making me feel sleepy after two years of helping with wakefulness. Any thoughts on possible reasons and approaches are welcome.

update: So far the following I've noticed have helped combat the sleepiness (in order of observed effectiveness - <insert super-anecdotal-warning here>). Thanks to all who helped, really appreciate it.:

• Drinking insane quantities of water
• Exercising right after Modafinil
• Noopept/Choline