Possible twins?

💗 • Girl mama x2💗 • Endo warrior
My HCG level has gone up really fast. 
August 19th -55 
August 21st -135 
August 24th -698 
I go for more blood the 26th and 28th. Twins run in my family. I'm also experiencing a lot of symptoms sooner than "usual" and with more strength. 
Any ideas?
I'm about 4w2d. 
Just curious as to what others HCG levels were!