@Pradeep
Your case seems like the girl already had an affair and not accepting you as her husband. May be due to her parents' pressure she married but ultimately left you within 3weeks.
Now technically there are two cases which lies with you. One is file RCR and second is take divorce based on cruelity as there was no consummation of marriage.
As rightly suggested by @Rohit Shukla, you should create proofs first. Keep sending letters, mails etc which you can prove in court. Let this activity ON for one month, and then file RCR. I'm sure to hinder your path they might back-fire with 498a but lets think positive and go like this.
Then as rightly stated by @kamal you will have to wait for one year and then you will have new ground called, desertion. No spouse can deny the other spouse to have the matiral pleasures emerging out of conjugal rights and to stay together.
Certainly people marry to maintain population and this is the most cherished institution wherein publically two humans can live together, have physical relation and form a family. But if one spouse negatives the effort of the other and take away such moments from other spouse, then the aggreived has all rights to get legally seperated from the erring spouse.
All the best!!
//peace
/Saurabh..V