In general, I think the following is a fair - if a bit strongly-worded - response to your question:
"It always makes me laugh when people hope they can learn physics online. Yeah, sure you can, just as you can learn languages online but you're not going to be articulate compared to someone that is on a full time course. They live physics for years with like minded people, day in, day out. If you want to learn physics the same way someone learns a foreign language by carrying around a translation dictionary because they lack the effort required, then go right ahead. Just don't delude yourself in believing you can know what a graduate physicist knows."
There is little substitute for a full-time course of studies if you really want to learn physics the way a young postgraduate / PhD. student knows the subject.
However, if this option is not currently available to you, or you prefer the out-of-class method / approach, the following may be useful:
The Road to Reality: a complete guide to the laws of the universe (Vintage, 2007), R. Penrose
An excellent "roadmap" / reading-resource book to guide you from basic* mathematics to advanced-level** physics.
(* As Penrose suggests in the Preface, the only prerequisites are a familiarity with [whole numbers and] the ability to do fractions.)
(** 'Advanced-level' physics means the frontiers of modern-day research physics, e.g. loop quantum gravity, string theory, twistor theory, dynamical triangulation theory, et cetera.)
The book is definitely NOT for casual reading: it may be best described as a roadmap for those pursuing a full-fledged undergraduate - then postgraduate - degree in theoretical physics.
The best way to utilise it is to*: [start from the beginning, then] (i) read a specific section of a chapter dealing with a specific topic (or area if relevant); (ii) find an appropriate textbook(s) to study the topic (or area) in full detail - with problem-sets and self-administered homework, quizzes, and regular tests to help you assess your progression; then, (iii) return to step (i).
Gradually, after several years, you should have mastered the requisite materials to understand a sizable fraction of research-level physics papers, et cetera.
(* In your case, as you already have some knowledge of undergraduate-level physics, the chapters pertinent to your interests may be more relevant.)
Also, the following online resource may also be helpful:
For online reading materials, et cetera: (there are many, so any sites which you might find helpful / useful may be added as you like)