Hi I know that Im really interested in anthropology and gender studies but theres also a completely different side of me that loves mechanical engineering and computer science.
Im pretty sure Id apply for anthropology but what if I wanted to change later to Engineering.
Is it possible given that my subjects in school are physics, computers, math & chem.
Im so confused any advice is welcome 
Yes. However, I need to point out that for some Universities (e.g. Penn, Columbia) it would require a transfer to the engineering school, so it’s not as easy as simply changing the major.
Yes, you can change majors. However it is usually more difficult to transfer into engineering than out of engineering, and engineerign normally has a larger number of courses that must be taken in specific sequence. This means that you should apply for engineering, and start there. Use your other interest to cover free electives and distribution requirements. Then re-evaluate your major in A vs. major in B options adter a semester ot two of college work.
Cornell Penn Columbia Princeton require being admitted to their engineering programs. The others admit to the college in any major, as does Stanford, Duke, Rice, UChicago.
Check out a school like Case Western Reserve University that has a single door admissions policy…once you are admitted to the University, you can major in whatever you would like and take classes in any of the colleges (Engineering, Arts and Sciences, Business). That is, you are directly admitted to a major and do not have to apply to move to Engineering if that is what you wanted to do.T hey have both Engineering and Anthropology. I majored in Electrical Engineerin but did a sequence of 4 courses in Anthropology.
RE #2:
"However it is usually more difficult to transfer into engineering than out of engineering, and engineering normally has a larger number of courses that must be taken in specific sequence. This means that you should apply for engineering, and start there. "
For OP, as a budding anthropologist, this is likely the case. But not necessarily for some others.
FWIW at my university, when I attended, almost all of the freshman engineering courses were fundamental math & science courses that had analogs in its College of Arts & Sciences (“CAS”) . A prospective physics major in CAS might well have taken an analogous course sequence to what the engineers took, save for a single “intro to engineering” course. If such student wanted to transfer to the engineering college they wouldn’t have much problem, course-wise.
That’s why those “3-2” engineering programs that a lot of liberal arts colleges have with engineering colleges can (theoretically) work. The students major in physics at the LAC so take a closely equivalent program to the engineers for their early schedule, knocking off the math & science prerequisite courses the engineering college requires.
Of course non-physics majors would not take this sequence. But realistically, how many prospective English majors will decide to switch to engineering?
Also, CAS had its own standards, with more emphasis on “soft” features, and didn’t accept just everybody for transfer.( Though the standards couldn’t have been all that rigorous, they accepted me !!) I wouldn’t know which college was more difficult to transfer into. I have heard often that at Columbia, for one, there is no free path from SEAS to Columbia College.
@monydad was your college an Ivy? If so, which Ivy?
Cornell.
Even at schools where there is no capacity limitation against changing into an engineering major, the sequenced prerequisite courses need to be started from the first semester in order to be able to change into or declare an engineering major and graduate on time.
In other words, your first year courses need to include math, physics, etc. suitable for engineering majors, as well as anthropology and gender studies courses, if you want to retain the option of changing into or declaring an engineering major.