I Had great clumping before I gave up shampoo, I just had it lower in my hair and it didn't go all the way to my roots. Some days it still doesn't.
If you want to keep your shampoo you could at least try a heavier conditioner or....... some days when my hair wouldn't clump well I added a little peach oil, or jojoba oil to my conditioner. I think my hair gets too clean and it doesn't always want to clump well.
Products help with the clumping too, like for me peach oil helps, aloe helps if it's in a conditioner, some gels seem to help clumping like herbal essence totally twisted. The products make a big difference in how well I clump and how well they stay together.
If you don't shampoo buildup can cause a lack of clumping too so it's a fine balance. At least it is in my particular experience.