I don't have much experience in employment advice area, so you should definitely take this with a (huge) grain of salt, but it seems to me that kind people who want to help you need to (as we say it in my language) pull words from your mouth with pliers.
You told us why you think you'd be proficient, but what you haven't told us is why you'd think that companies you applied for a job would think you're proficient enough to do the job.
You haven't told us what type of positions you applied for and what type of companies you applied for. You haven't told us anything about what type of impressions you think you left during interview (and we don't know if you even got to the interview phase and if you did, to which sub-phase you got to).
Sometimes hiring patterns may look extremely strange to outsiders. For example some agencies in my country are basically family run businesses and when they're hiring, they already have candidate in mind before process even starts, so you basically need not apply. Some other companies only hire graduates from certain universities and that becomes visible only after you analyze their employees for a while.
Some companies may want a level of "focus" from their candidates. For example I've been a witness to analyses of CVs for a marketing position in a company. A candidate finished engineering related secondary school and then moved on to undergraduate economics studies, but not in marketing before finishing marketing masters. That was judges as too unfocused. Seeing you finished both physics and electronics engineering, some people may think that you're a jack of all trades and master of none. Back to the company example: Another candidate's problem was that he didn't look "refined enough" even though he had needed experience. Sure, that type of job requires more people skills that engineering, but I wanted to use it as an example of non-obvious requirements.
Since I'm talking about "people skills" how good are you with that? Do you fit with local expectations? Can you easily explain to others what you think? Some data about communication with companies would be welcome here. Once again, I'll mention two diplomas: to get them, probably means you're very smart. That can sometimes be a problem if it's some lower level manager that does the interviews. He might be intimidated by you! Also have you been "networking" with people in same position? What do other recent graduates from your schools say? Are they having problems finding a job as well? What are their experiences?
You also mentioned that you're a recent graduate from an university, but you didn't write more about that. Are your grades good? In some areas some employers may pay more attention to grades than real experience. Opposite of what I wrote can happen as well. If you're too good, some companies may avoid you. Sometimes it may look like a better idea to hire an average Joe who will be happy with the job and work for years than a genius who will find the job bad and want to move on as soon as he learns the basics.
One more thing I'd like to ask you if how long have you been looking for a job? Perhaps it just takes more time to find one than you expected. Are you aware of how things are going in your local jobs market? If you haven't already, try looking up some statistics and see how well you're going. It could be that the job marker got saturated quickly by large amount of new graduates for example. One more thing that could happen is that companies got used to an "employer's market" where they could pick right candidate from a sea of very experienced candidates and the sea quickly drained up without the companies noticing it. That happened in few areas in my country and for a while nobody could get hired until the companies realized that they can't hire a guy with decades of work experience for a beginner's salary.
As I said, I don't have much experience in looking for a job, but keep in mind that the more information you provide, the greater are the chances that someone could give you helpful comments.
Finally I wish you good luck in your search for a job!