Slow Rising Bread

Hello

I am a complete beginner in the sourdough world. I am a low budget mamma and can't really buy a established starter; moreover, The Netherlands is a rather difficult place to get nice flours (can you imagine they don't sell WWFlour in the supermarket?!?!?!). Therefore, i started my own, with the instructions of Mike Avery in his site sourdough home, 2 weeks ago. Started feeding it every 8 hours, on a basis of Rye and WW, and from the beginning it always smelt so good. So far it has been bubbly and happy, and after the first week I switched to feeds every 12 hours with rye and AP Flour. It started to double its volume by then. With all these signals of health I decided to jump in the pond. I took a recipe of Pain de Mie I found in the Sourdough Companion site, because it seemed easy. It prompted to make a sponge with 1 T of starter (I used 3, though, just to "give more power") and 100gr flour and 100gr water. I left it overnight, and this morning it had bulked considerably. I proceeded to mix the dough ingredients, amongst which there is milk and butter, I kneaded 3 times with intervals of 5 min, 5 min each kneading, then fermented for 3 hours with a fold each hour, until it seemed to have doubled even though I had my doubts. Here things started to seem slow, since in the recipe it said that it would take 2 hrs the first rise. I punched down and shaped in a tin the half and the other in a "log". It's been 3 1/2 hrs and my loaves seem to be so slow...! They haven't doubled so far, and I am wondering if this is normal. Is there anything I might be doing wrong?? I am patient, but I wonder about the average rates of rising for sourdough. I hope anyone can help me with some answers.

Grateful in advance,

P