Hi, 
Welcome To HCM & Thanks For Asking Your Query Here 
As you said your platelets count is okay but still you are having severe nose bleed , so in this case it is not related to low 
platelet count and there are many other medical conditions which may be cause this including
exposure to warm, dry air for 
prolonged periods of time, nasal and sinus infections, 
allergic rhinitis, vigorous nose blowing,if u had any nasal surgery,
it may also be a result of deviated or perforated nasal septum
and it needs thorough medical check up and investigations to spot a confirm diagnosis 
blood clots from stomach are related to the 
nasal bleeding going down into stomach
finally i would strongly suggest you to see an 
ENT specialist ,with thorough medical checkup he may go for all necessary medical investigations to rule out any underlying medical condition
I hope it help 
Thanks & Get well Soon