Selective androgen receptor modulators or SARMs are banned under the World Anti-doping Agency proscribed list. Further more they are prescription only medications meaning that selling these medications could be a criminal offence with a 14 year sentence.
The advantage of doing two runs in a day is that you can either run at a higher intensity for longer (two fast runs instead of one slower paced run). This would be an advantage if you are looking for speed over stamina.
Alternatively you could target two different pace zones; easy pace in the morning fast in the evening. This would be more of a long term plan as two intense sessions per day is asking for an injury.
I would suggest that two intense sessions would be OK in the build up to a 5k or 10k race.
Doing two sessions per day and a long run at the weekend sounds like a great plan to me. What are your objectives? Race? General fitness?
I was thinking the same thing, the symptoms don't quite seem to fit but try taking an antihistamine when the symptoms appear. Try a quick acting one like Chloraphenamine (Piriton) and see what happens. This medication will normally make you feel drowsy btw. if it eases the symptoms then next step would be to try and work out what is causing it. If it has no effect then it is unlikely to be an allergy. Can I ask how old you are?