Anthony,
It's pretty impossible not to have side effects on HT, although there are loads of them and no one gets all of them. It depends on the person, and on the HT drug being used, and it varies during the course of treatment.
You haven't put up any details of your diagnosis in your bio, so I can't really comment on if any of the symptoms are likely due to the PCa, but it's unlikely any PCa symptoms would get worse during your first 3 months on HT (unless you are on a HT drug which starts with a testosterone flare and you didn't take an anti-androgen such as bicalutamide while you were starting the HT drug).
HT does affect joints and ligaments in some people (most commonly hips), and it could be due to that.
Some of the things you describe also happen to people without PCa and not on HT, so they might be completely unrelated.
If the hot flushes bother you, there are some things you can try.
Keep a diary of when they happen, and try to identify common triggers. If you manage to do this, you can then try avoiding whatever it is that triggers them for you.
Dress cool. Use layers which you can throw off to cool, or tops with zips you can easily undo to cool off.
Some people find acupuncture works for them. Some of the prostate cancer support groups and Macmillan centres in hospitals offer this for free to patients on HT.
If none of these work for you and you feel you really need to do something, there are some drugs your GP or oncologist can try which help in some cases, but they are not without side effects of their own, and GP will need to carefully monitor your liver function as they're toxic to some people. Medroxyprogesterone is a drug which you may be able to try for 10 weeks, and continue with if it works and your liver gets on with it. If it fails, there's also cyproterone or megestrol which you might try. If you start suffering from gynecomastia (breast growth), the tamoxifen given to avoid/reverse that also seems to prevent hot flushes in some people, but it's not prescribed for hot flushes alone.
If the hot flushes are not a serious problem for you, then it's better to avoid the drugs.
For tiredness, I suspect exercise helps. Again, many of the Prostate Cancer Support Groups run exercise classes, often free or low cost. However, you should supplement these with your own - at least every other day go out for a walk. Exercise is very important on HT anyway, and talk with your GP about taking calcium and vitamin D supplements with the exercise to keep your bones healthy while you are on HT.
I don't know if you're on HT for a fixed period or for life, but if it's a fixed period, you might want to try and preserve your erection function which is easily damaged by not having regular erections due to loss of libido on HT. Quite a bit has been written on this in this forum, but basically, you mustn't allow loss of libido to stop you having erections, or you may find they don't work when your libido recovers after you finish HT.