Hi Rose, and welcome to the Forum. It's a great place to understand not only your Sheltie but also to get feedback and advice on pups in general.
I so know what you are going through. My Timber died in May with a tumour and I brought home Bacca just about 6 weeks later and I couldn't remember anything about puppy 101. I jumped on the internet, hauled out my old books and just read, read, read!
Do you live in an apartment or do you have a yard? That's my first question, because it will make a difference in how you manage house-training.
My first recommendation, if you've not already done is is crate-train the pup. Crate-training is not cruel nor is it intended to be a "cage". It is the pup's private den that he can go to when he's tired and needs to chill out. The advantage to crate training is that pups will rarely soil in their crate, therefore learn to "hold it" for longer. Makes house-training go a whole lot faster! I won't go into the particulars of crate-training in this email, but if you do a "search" on this site or on google, you'll get tons of info on how to go about it.
If you are an apartment dweller, I can't help too much, because I've never had to use pads or paper to train. The only thing I can add though is that when pup is outside his crate, you must watch him all the time, until he becomes reliable. I think it took Bacca till about 12 weeks before I could trust him out of my sight for more than a few minutes.
Also, regardless if you are paper training or outside training, stay tuned to pup's schedule. Pups will normally want to pee as soon as they get up, 5 or 10 minutes after they eat, when they get up from naps, after playtime, and certainly before bed. Some pups need to go out in the middle of the night but with a crate that generally goes away very quickly.
So when you say that Trevor seems to pee alot, that's totally normal. I think at 12 weeks, I was taking Bacca out 8 to 10 times per day. Just to be safe! And to praise and treat him when he did his business where he was supposed to.
Now Bacca is 10 months (and I now also have 10 month old Indy). They could both probably manage with going out 2 or 3 times per day. I take them out more, because I can.
Hope this helps!
Don't be shy about posting to the general forum for more answers! You'll get lots of love and support as you and your pup grow together.
Take care
Barb