Guitar feedback problems?

i have a line 6 spider 4 15 and a mexican fender strat, not squire. im having really bad feedback problems. its not the chord ive tried many. ive also noticed when i tilts the guitar differently the feedback changes. when the strings are facing the amp the feedback goes down and the feedback gets worse whenever i tilt it away. i just went to guitar center and i played on the same amp and there was absolutely 0 feedback. its starting to piss me off. so is is t eguitar or amp and what can i do to fix it?