On the flip side to the comment above, there are advantages.
You said you are a confident traveller, so it's not going to be like you can't find your way around a train station or you're going to worry about timetables and the likes.
Travelling solo will give you the opportunity to do precisely what you want to do, go where you want to go in your own time.
You will have the chance (if you so desire) to meet new people at the various hostels that I assume you are staying at.
It could get somewhat lonely, however, given that this is only three weeks, it isn't that long; and just make sure that you either catch some sleep on the train, or/and ensure that you have magazines or/and puzzle books to complete on the long journeys where you might otherwise have just talked to your travel buddy.
You just have to make sure that you look after yourself, and that you don't put yourself into dangerous positions, and certainly take advise when you get to the hostel about what areas you should avoid.
Have Fun !!