I can write some tasty riffs but I seem to have trouble turning the catchy riffs into an actual song.

I can make a good main chorus riff but it's hard make another riff that connects to it. Once in a while I can bullshit a verse with a riff but when I can I still can't make it into a whole song. Everything I write seems repetitive and I don't know how to make the part of the song that holds everything together.

Any tips? I'm not super educated in theory, I know some chords and scales but don't really know what to do with them or how they would help.
Don't force anything that's not there yet.

I stole this idea from Mark Tremonti, it's so simple but brilliant, and it's been working so far because I was having similar issues piecing an entire song idea together with riffs I've come up with. Whenever I come up with a riff or chord progression, I try to figure out what it'd work best as (intro, verse, chorus, bridge, etc) and then I'll record it and put into its appropriate category (with its tuning too since I use an array of different tunings) in a spreadsheet on my laptop and then you basically just stockpile ideas for awhile. Once you have enough possible intros, verses, chorus's, and bridges, you can start combining them and see which ones naturally work together and can be a possible song. This method works best if you have a lot of ideas. As long as you write often and record everything you do, that shouldn't be too hard. There's nothing wrong with hoarding ideas and riffs until it comes time to put them to use as long as you do put them to use eventually.

It's like a puzzle, you just have to find the right pieces that fit together. That's how I look at it anyways.