Hi coldethyl - no-one has to take HRT but we all balance the pros and cons, risks and benefits, quality of life etc, depending on our own medical history, family history, our jobs, our general health and well being etc.
So - in your case - if there is family history of osteoporosis and you have been peri-menopausal for some years then you may be at increased risk of this. How long your cycles have been erratic will give you an indication of how long you have been in peri-menopause and how much oestrogen you might have been lacking. If you are worried about this in particular you should be able to ask your doctor for a DEXA bone density scan. I expect you've already looked up about osteo but there is basic info on this site (middle health tab above - which also gives the risk factors
http://www.menopausematters.co.uk/osteoporosisrisks.php). There is also the National Osteoporosis Society website. Calcium supplmenets alone won't prevent osteoporosis but are obviously important as well as weight bearing exercise.
For those with early menopause then HRT is advised to help protect against osteoporosis, until the average age of meno of 51/52.
Having migraine with aura is not a contra-indication for HRT - transdermal HRT is recommended instead.
Migraine
Migraine is often triggered by hormonal fluctuations and therefore may occur around the time of a period. Such migraine may improve at the time of the menopause. Some women find that migraine may be triggered by the daily hormone fluctuations which can occur with oral (tablet) HRT so the transdermal (patch or gel) route is usually preferred with a history of migraine. http://www.menopausematters.co.uk/atoz.php#GlossMIf you have endometriosis then this can be problematic but you can still take HRT but you will need a continuous progestogen - and this is what sometimes causes more of the side effects with HRT, This is what it says:
There is a small risk of reactivation of endometriosis with HRT use and any recurrence of symptoms should be reported. If a hysterectomy has been performed for endometriosis, the choice of HRT use thereafter should be influenced by the extent of endometriosis at the time of the operation. Since hysterectomy often causes a premature menopause, it is often advised to take HRT until the average age of the menopause; 51 years. HRT after hysterectomy usually consists of estrogen only. However, in the presence of endometriosis, estrogen may cause stimulation of residual deposits and consideration should be given to using continuous combined (estrogen plus daily progestogen) therapy, or tibolone, though little research has been done on the effect of different types and duration of therapy. Medical treatment of endometriosis often involves ovarian suppression which, along with ovarian removal, may increase the risk of osteoporosis. http://www.menopausematters.co.uk/atoz.php#GlossEI would suggest you ask for a dexa scan and take it from there.
Almost all women can take local oestrogen for the "shrivelling lady bits" for an indefinite period so if you are suffering here then also ask your doc for Vagifem or similar!
Hope this helps
Hurdity x