Since you're AU on your sister's card, which is presumably 6 months or older, you should be back on the credit grid now.
The credit bureaus and FICO don't keep a calendar going that says that in April, you had no current history, so by golly, it will be October before you exist once again. All they know is that once there is an account there (your sister's), which is older than 6 months and has been used within the last 6 months, then congratulations, you exist once again! (Or you should.)
I agree with the others: use this opportunity to get at least one card in your own name. You need to determine when the next statement posted (or will post) after you added on, and give it a week-10 days for all the credit bureaus to display it on your reports. Then pull at least one to confirm.
Since a quick review of your reports will show a lender that this isn't really your credit, I would go to several local credit unions in your area, explain what happened, and ask if they would be willing to issue you a card in your own name. As most credit unions use Equifax (EQ), I would pull your FICO EQ report to assure yourself that you now have a score. Print it out and take this score report to the CU's, point out that it's FICO, and ask for their opinion. (Be sure to say that you are NOT authorizing a hard inquiry at this point!) When you find a place that you like, go ahead and let them pull your report themselves (there's your hard inquiry) and them presumably offer you their card. They might offer you a secured card, which is fine, but do ask if they will convert it to unsecured after a set period of time, and if you will keep the original issue date. Unsecured is better, but secured will work.
BTW, even though I'm pretty allergic to AU cards except between spouses and long-term couples, I think this is a great reason to use one. OP did once have his own credit, but there's nothing current, and he's going for a mortgage. This gets him in the running.
"Bilgefisher"? You have fish in your bilgewater?
sounds icky...
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007